Photo-induced resistivity change p has been studied in perovskite manganite La2/3Ca1/3MnO3 thin films with a continous wave laser and modulated laser pulses in this paper. Experimental results show that in the sample films, the maximum of photo-induced resistivity change（ΔR/R）max can reach 43.5%,which is a very exciting figure in this research field. Modulated laser pulse induced signal intensity has a highly nonlinear relation with the applied current and temperature. The maximum of photo-induced resistivity increase is a second power function of the applied current, while the temperature at which the maximum appears is proportional to the bias current. There exist an optimal bias current and a temperature for optical response in this film. These results are attributed to the optical excited eg↓ carriers and polarons.