The thermodynamics of La_0.7Ca_0.3MnO₃ film by terahertz transient spectroscopy were presented. The temperature of metal-insulator phase transition of La_0.7Ca_0.3MnO₃ film is observed to occur around 260 K， which is almost the same as that of the ferromagnetic-paramagnetic phase transition. It indicates that the conductivity of the La_0.7Ca_0.3MnO₃ film is closely related to the order of magnetic moments in the film. We find the conductivity of the La_0.7Ca_0.3MnO₃ film can be reproduced with Drude model at low temperature range from 40 K to 200 K， and Drude-Lorentz model at high temperature region from 210 K to 290 K.