Abstract: A diagnostic system of working conditions in wells with single screw pumps consists of two parts, i.e. data acquisition and data analysis and optimization. It can perform real time monitoring of downhole working conditions in wells with single screw pump and provide timely parameters such as rotating speed, torque and load of screw pump. These parameters can be optimized through comparison with their theoretical values. This paper introduces the installation and application of this system and presents some proposals concerning improvement of this system.