With pump-probe method, the photocycle of bacteriorhodopsin is studied in two sets of measuring systems which have different time resolution and exciting mode.One is carried out by a single shot pulse Xenon lamp inducing the purple membrane suspension sample. The other is performed by a repetitive Q -switch double frequency Nd : YAG laser periodically exciting the sample. The testing beam for the two systems is a 633 nm He-Ne laser. An avalanche photodiode is used to detect the probing light passing through the sample when pumped by the actinic light. The picked up signal is coupled into a 500 MHz digitizing oscilloscope which measures and processes the BR's photocycle response signal. The experimental results indicate that the period of BR photocycle is less than 15 ms, the time constant from K to L is 2 μS, the relaxation time from L to M is 50 μs. A doubtable component is found occurring prior to K. Based on the emasured data, a model of the bacteriohodopsin photocycle in the time domain from nanoseeond to millisecond is proposed.