The toxic mechanism of element mercury,methyl mercury and mercuric chloride,which were the main chemical speciation in soil,were analyzed.And the exposure pathway to human body of different chemical speciation mercury was clarified.The risk control values(RCV)of different chemical speciation mercury were calculated according to related model and parameters in the Human health risk assessment technical guideline of our country.Then the calculated RCV of three kinds of mercury in soil were compare to the RSL(Regional screening level,RSL)of USA,similarities and differences between them were analyzed,and the reasons that induced the difference was discussed.The research results suggested that,the main hazard of mercury to human was non-carcinogenic effect.Elemental mercury(Hg)mainly through respiratory breathing cause harm to human body,and the exposure pathway were inhalation of soil particle contaminated by mercury,and inhalation of mercury vapor,which was the main exposure way of elemental mercury.Methyl mercury mainly through oral intake cause harm to human,and the main exposure pathway was ingestion of soil.While,the mercuric chloride can cause harm to human body via oral intake and inhalation,and the exposure pathway include ingestion of soil,inhalation of soil particles,the vapor intrusion exposure way doesnt exist because the mercuric chloride cant produce vapor.The calculated RCVs of three kinds of mercury were mercury element 0.04 mg/kg,methyl mercury 8.39 mg/kg,mercuric chloride 24.9 mg/kg.The RSL corresponding regional screening values of three forms of mercury were: mercury element 10.1 mg/kg,methyl mercury 7.82 mg/kg,mercuric chloride 23.5 mg/kg.The RCVs and the RSLs were compared and the similarities and differences were analyzed,the results show that the calculated RCV of Methyl mercury and mercuric chloride are similar with RSLs of US.The reason was that Methyl mercury and mercuric chloride had the same exposure pathway to human body.And the reasons that cause the subtle difference were that the human characteristic parameters are different between China and USA.The difference between calculated RCV of element mercury and RSL of USA was very big.And the reasons can be divided into two different aspects.First,the exposure pathway was different.Inhalation of indoor mercury vapor and outdoor mercury vapor were both considered when the RCV of element mercury was calculated.But the RSL of USA doesnt consider indoor or outdoor vapor.And the calculation of element mercury RCV indicated that inhalation indoor vapor had more harm to human health than inhalation of outdoor vapor.Second,the migration-diffusion model that used in calculation of RCV was Johnson & Ettinger model,but in the calculation of RSL,the migration-diffusion model was Q/C model,which indicated that the difference in model selection might be the most important reason induced the big differences between RCV and RSL of elemental mercury.So,it was suggested that the chemical speciation of mercury should be detected when we carried out the investigation and assessment work of mercury contaminated sites,in order to make the assessment results are more accurate.And the chemical speciation of mercury should also be considered when calculating the RSL or determine the remediation goal of mercury.