The fast development of the Graphics Processing Unit’s programmability and parallel computing power provides new solutions for visualization technology. Using ray-casting, a CUDA based interactive volume rendering tool is realized. Several rendering effects have been implemented, including alpha blending, iso-surface rendering, maximum intensity projection and X-ray projection. In order to improve alpha blending and iso-surface rendering effect, a per-pixel based Phong Lighting Model is added in. The experimental results show that the tool can make use of GPU's parallel computing capability and render high quality image. It’s interactive and extensible.