Volume rendering requires too long time to generate a high-quality image. Even though there are many sampling points in a volume space, many of them do not contribute to generate the final light intensity of pixels. This paper proposes a approach which reduces the load of the sampling processing on the operation level and shows the implementation results with volume data. The results show that the approach is 1.33~1.78 times faster than traditional approach. The approach is characterized by reducing the time complexity of shading calculation and shading composition.