During the oil production, in order to monitor the working conditions of an electrical submersible pump (ESP),an electrical current recorder is used to monitor the electric motor current of an ESP.The recorder charts indicate various working conditions of the ESP. Subtle malfunctions or abnormal problems of the ESP can be detected and further analyzed from various features of these current curves on the recording charts. Presently, these current charts are manually read and analyzed in oil fields. In this paper, a diagnosis expert system is presented for automatically analyzing these current recording charts and identifying the working condition of the ESP. This expert system includes an open knowledge base, which can be updated or enriched according to the identified features of the current curves on the recording charts, and a condition monitoring and failure pattern recognition method, which is called "pick-up method of feature of the recording chart", and can be correctly applied in most cases. It has been shown that this expert system can effectively improve the accuracy and efficiency of failure diagnosis and working condition monitoring of ESPs.