Abstract: A passive resonator laser gyroscope system composed of a reflective ring cavity is reported in this paper.The structure of the passive resonator is different from ordinary passive resonator:(1)there is only one lens in ring cavity to decrease the total loss of the cavity and to obtain much narrow resonative line width;(2)the intensity of the reflective light and the transmission light are minimum and maximum at the resonant centre respectively,so the SNR of reflective light can be greater than the SNR of transmission light;(3)the structure of the system is the compatible with passive resonator optical fiber gyroscope.The system has advanced performance,and its stability of drift is 1.7degree/hour in lab environment.The majoy reason causing drift is noise and closed loop control error in control circuit.