This paper presents a novel auction-based structure to multi-robot coalition formation problem. The structure, which is called multi-robot Coalition Structure Generation based on Credit Mechanism (CoSGCrM), contains a sub-optimal coalition member selection algorithm with an analysis of its soundness and completeness. A credit mechanism is introduced to reduce the complexity for the coalition leader in making a decision as well as to restrict the profit-oriented robot member in bidding for coalitions. Simulations are given to compare with first-price auction algorithm and the results show the viability of the proposed structure in both simple and complex tasks environments.