Considering optical thin films irradiated by laser at oblique incidence, the electric vector is orthogonally decomposed into s-polarization and p-polarization. And based on the Maxwell equations, electromagnetic-field distribution in optical thin films is obtained. Then the optical properties of optical thin films are numerically analyzed. The results about high-reflection thin film show some features as follows. With the increase of the angle of incidence, the reflectance, transmittance and absorptivity of s-polarized light have tiny fluctuations. But for p-polarized light, obviously, the reflectance shows gradually decrease while the transmittance and absorptivity are opposite. And near the central wavelength in high-reflection thin film, both s-polarized light and p-polarized light have a high-reflectance broadband. Compared with s-polarized light, the broadband for p-polarized light is manifestly narrower and the absorptivity is relatively higher.