The target of our study is to set a new cost model to solve the partial postponement problem by adding penalty cost parameter of shortage under stochastic demand. By doing this, we hope the new model can be better applied to real conditions. Postponement is an important strategy to achieve mass customization and it has been adopted by many companies to improve production operation, inventory and logistics management and supply chain operation, but the postponed activity will cause additional costs at the same time. There have been many literatures trading off between the relative cost and the postponement benefits of product manufacture, and our paper is to solve the similar problem.