Focus on the illumination coherence problem of the three-dimensional virtual scene, the environment mapping technology was analysed to improve the reality. The light probe image is used to light the scene and the irradiance of the diffuse surface is approximated by using spherical harmonics. By considering the shadowed diffuse transfer simultaneously, the soft shadow of diffuse objects is generated successfully under dynamic, low-frequency lighting environments. It is showed that this algorithm approaches accurately with high quality.