The quantitative intensity dependence of photobleaching rate has become crucial in elucidating the photobleaching mechanism.The two-photon excitation(TPE) photobleaching lifetimes of single rhodamine B(Rh B) molecule excited by femtosecond pulse laser with different intensity were measured using the MRC1024 multi-photon excitation fluorescence microscopy system and the single-molecule counter.Experimental results show that the photobleaching lifetime of single RhB molecule with TPE depends on the two-power of the intensity of excitation laser,implying that the photobleaching rate depends linearly on the probability of single dye molecule in the excited states.The result is consistent with photobleaching results with one-photon excitation(1PE),but is different from that of ensemble photobleaching with TPE.