Abstract: A practical face recognition system makes high demands on accuracy and real-time.The eye-pupil locating is a key factor which effects recognition rate and efficiency.In this paper,an eye-pupil loacating method based on adaptive threshold changes is proposed.The eye pupils are located by the threshold changing,similarity analysis,natural constraints condition and gray centre of gravity according to the idea of MER (minimum extremal region).A lot of experiments are done on CAS_PEAL,CVL and self-construct face database.The experimental results show that the method is effective and has a high locating rate.And the method is robust for variant illumination and face expression.