Underwater optical effect simulation is an important part of simulating natural scene. However, computing these effects is difficult and time-consuming, since light refracts when passing through waves. To address the problem, this paper proposes a simple and quick method for rendering underwater scenes, including the shafts of light refracted by the dynamic water surface, caustics caused by the effects of light and shadows beneath the creatures in the water. The method simplifies the Iwasaki?s method to save the computation-time by an eye-irrelative method calculating the intensities of the illumination volumes with parts of intersection points of Iwasaki?s. As the experiment results show that our method got a high frame rate with an acceptable quality for real-time applications.