The properties of limitative capacity of material supplier, special design and hardly shorten chemical product process cause integrated circuit (IC) assembly industry need to take more high risk and cost than other kind of semiconductor industry to cover the loss of bullwhip effect. In this study, we focus on analysis the prosperities of material suppliers and purchasing process and find out the limited factors and using theory of constraints (TOC) to rebuild the original purchasing process model. The TOC purchasing model is implemented between a local IC assembly company and three different material suppliers. The results show that the model can improve the efficiency of purchasing and provide a reference of purchasing supply chain management.