There is no provision on the terms of“a friend of the court ” in the law of mainland China，which does not prevent us from learning from the system of “a friend of the court”.And the concept and scope of “expert assistant” and “expert assistants ” in China’s procedural law have the same and different aspects of“a friend of the court”.
　　“A Friend of the court” is rended as “Amicus curiae” in Latin which originated in ancient Roman law.Amicus curiae refers to the opinions submitted to the court by natural persons，legal persons or other organizations other than the parties for the purpose of assisting the court to make a fair decision.
　　The amicus curiae system was first introduced by Britain.Amicus curiae can be applied to the following three situations in the United Kingdom： the first is that court accepts a major case that may affect the interests of a large number of people other than the parties to the case，The Court may invite the Attorney-General as “Amicus curiae”； The second is to prevent the court from making an unfair decision，and the third is applied to the situations that the absence of or the further defence of a party at the hearing.
　　Amicus curiae has failed in Britain，but thrived in America.In the case of Green v.Biddle in the early 1920s，the attorney general of Kentucky participated in the trial as the first “ Amicus curiae ” in American history.Since then，the U.S.government began to participate in the proceedings as a “Amicus curiae ” to safeguard the interests of the public.Later，individuals，social organizations or interest groups were also allowed to participate in the proceedings as “Amicus curiae”.The“Amicus curiae” system has undergone several changes since it was introduced into the United States.Although many outsiders can participate in the trial as “ a friend of the court”，they are not the parties after all，and the judge results have no direct interest for them.So it is impossible for them to enjoy the same rights as the parties.The US law has a strict time limit for the filing of the“Amicus curiae ”，which means that it is not ok to file the“Amicus curiae” at any time，but in the application for the review order of the case and the trial stage of the case.This time is not allowed to be extended.
　　There are some differences between “A friend of the court” and “appraiser ”.The litigation status of the expert in the criminal proceedings in our country is “litigation participant”.And the litigation status of th “A friend of the court” depends on the situation，sometimes，is the litigation participant，and sometimes is not.The way of the participation of “A friend of the court” is rather loose； The main participants of “A friend of the court” is different from that of the “appraiser”.“A friend of the court” can be a natural person，a legal person or other organization，while the “appraiser” must be an individual. 　　There are some differences between“A friend of the court” and “expert assistant” Sometimes the litigation status of “A friend of the court” is the litigation participants，and sometimes is not .However，our “expert assistant” is not the litigation participants.“A friend of the court” can be a natural person，a legal person or other organizations，while the auxiliary expert must be an individual.“A friend of the court” can take the initiative to apply to and participate in the court and also can be invited by the court，but the “expert assistant” is involved in court by joint application of the public prosecutor，the parties and defenders，the litigant agents of both sides.“A friend of the court” can either submit a written statement or oral defense to participate in cases，while the “expert assistant” only give oral advice to participate in the proceedings.
　　“A friend of the court” has several important functions，that is，it can guarantee the fairness of cases，improve the efficiency of judges in court trials，and fill the gap of the lack of professional knowledge of judges and other judicial personnel in specific fields.Moreover，the “A friend of the court” system broadens the channels for the truth of the case and correct application of the law.This system also provides a more sufficient and reliable basis for the court’s judgment，and thus ensures the substantive justice of the judgment.
　　作者簡介
　　黄依琳（1993—），女，汉族，山东省，在读研究生，青岛大学，研究方向：诉讼法。