By analyzing the DWT's polyphase representation and GPU's general-purpose computation model, this study presents a 2D DWT algorithm based on GPU and polyphase, which combines with modern GPU's multi-texture property and multiple render targets property. The computing form is well suited to GPU's SIMD architecture in the method presented. The number of texture visit is significantly reduced. The GPU's vector processing ability and 2D address accessing ability is well utilized. The experimental result shows that the processing speed is greatly improved.