Abstract: For sand control wells, gravel size affects directly the sand control effect and the well production performance. So gravel size is the key step of gravel-packing sand control completion design. Due to the unclear description in original documents, the difficult computerization of its design process and the blurry scope of the corresponding parameters, DePriester model, as a widely used gravel size model abroad, is not universal in China unfortunately. In this paper, DePriester gravel size model is re-derived, some unreasonable considerations in the prime model are also corrected and the values of some parameters are recommended. Finally, a computer procedure for DePriester gravel size model is put forward, which is implemented in software. DePriester model depends on the sieved curve of formation sand and is feasible for non- uniform sand especially, and under which Saucier model is not applicable.