By using of the Rifs (Reflectometric Interference Spectroscopy) system and the testing result of AFM (atomic force microscope), a novel method for directly monitoring the change of reflectometric spectrum extremum during antigen-antibody interactions is proposed. Experiments show that the process of immunoreactions can be directly monitored and the results can be saved continuously by this method. Compared with film thickness extremun method, this method is simple, sensitive and effective for immune dynamics study.