The 3-D DCT is different to be described by mathematical expression, and the transform is accomplished by computing 1-D DCT to each dimension of 3-D signal successively, which cannot embody the overall space character of 3-D transformation well. To overcome such drawbacks, a SDCT method was proposed in the paper. First, several 3-D matrix operation methods were defined, and the transformation basic matrix was build. Then, the operation principle of 3-D SDCT was described in detail. Finally, the 3-D SDCT operational performance was described. The theoretical analysis shows that the SDCT makes 3-D DCT succinct to express, easy to comprehend and convenient to operate.