According to supply chain management, the balance between the supply capability of products and the cost of inventory should be achieved in enterprises at the chain. It is important to the nodded enterprises to analyze the supply capability of products. On the basis of the credibility theory, the concept that the supply capability of products should be measured by fuzzy demand was put forward, the formula to compute the supply capability and its practical examples were given and the effects of changed membership functions on the supply capability in fuzzy demand were discussed.