This paper presents an image-based real-time rendering algorithm on GPU. By the algorithm, we uniformly sample an object in all directions in a polar coordinates system, to construct a Spherical Depth Image. With two deduced Warping Equations, we then pre-warp the image onto a view-dependent tangent plane of the bounding sphere of the object to get an intermediate image, which can be further rendered onto the target image plane using standard texture mapping. By exploiting the inherent parallelism of modern programmable GPU, we transport the pre-warping process into Vertex Shader. Furthermore, the hardware pipeline's rasterization function is utilized to conduct the image re-sampling efficiently to generate hole-free rendering results. Besides, Per-pixel lighting and Environment mapping effect is implemented in Pixel Shader to get high quality lighting effect. Finally, we solve the problem of limited field of view, and design a LOD (Level of Detail) algorithm to implement a real-time walkthrough system, in which all the rendered objects are occluded by each other correctly.