The pump-probe method was used for measuring the transient change of optical transmissivity of metal particle-matrix composite thin film Cu-Ba-O exposed to ultrashort laser pulses. The phenomenon was observed that the optical transmissivity in the thin film rapidly decreased and then recovered in a few picoseconds. The optical relaxation is a process in which nonequilibrium electrons, excited by laser pulses and originating from near Fermi level in Cu ultrafine particles, return to the equilibrium state. An amended theoretical value of electron-phonon coupling constant g of Cu ultrafine particles in the composite thin film was given.