In this paper, a partial cost intra prediction algorithm based on transform-domain property is proposed. After transform processing, the intensity of the whole block is collected into the first few pixels. The differences in the low frequency region are adopted to represent the total distortion of one 4x4 block. In comparison to the previous fast mode decision algorithms, which mainly reduce the number of candidates in the RDO process, the proposed algorithm simplifies the computation in the cost function. Moreover, the integer transform with cosine multiplication is applied in the proposed algorithm and gets better results in intensity collection. With the benefit of linear transform, the number of operations is further reduced approximately by 40% of the original cost calculation suggested in H.264 JM standard.