ZnSe films with thickness from 0.045μm to 1.4μm were grown by MBE on (100) GaAs substrates and characterized by room temperature Raman scattering. The relationship between the coherence length L and the qualities of ZnSe films was analyzed from the line shapes of the first-order longitudinal-optical phonon Raman scattering quantitatively. The shift asymmetry of the LO phonon peak was investigated in detail. The results show the quality of ZnSe film is gradually degenerated with the decrease of the film thickness. This is attributed to the lattice misfit-induced imperfection in epitaxy layers. This result coincides with the experimental one.