The coated PP films were produced by the means of overlaying. In the experiment, the solutions of the sorbitan monooleate with different concentration were coated on the PP films. The light transmittance and the mechanical property were tested after the water bathing, which were compared with the PP films without coating. The results indicate that the light transmittance of the coated films was higher than the films without coating whose light transmittance was 93.24%. When the concentration of the Sorbitan Monooleate was 12%, the light transmittance was up to 96.03%. In addition, the mechanical property of the coated PP films was raised. The analysis of infra-red spectrum indicated that the ester group could hydrolyze into hydrophilic group during the hydrolyzing. This could improve the surface tension of films. Therefore, the overlay played a big role in the improvement of light transmittance.