To solve the slow rendering problem of ray tracing algorithm in irregular scene, an improved grid subdivision ray tracing algorithm was proposed based on the in-depth study and comparison of the recent acceleration algorithms of ray tracing. First, the rectangular bounding box of the scene was set to remove the influence of external light, and the intersect operations was simplified; second, spatial grids were created with a new way to limit the spatial unit number and complexity of storage space within a certain range; finally, the traditional spatial grid algorithm was greatly improved by subdividing grids to eliminate the bad influence on acceleration effects due to ignoring some blank space. The experimental results show that this method can effectively improve the light speed in blank space, it not only increases the time efficiency but also reduces the space lost.