Research of the way of business process re-engineering (BPR) has been one important task in the field of e-government and government information. One method of BPR on the process of purchasing and bidding, based on interpretive structural modeling (ISM), is proposed in this paper. With the aid of this method, business process is converted into the structure model, and then redundancy and deficiency are mined. After qualitative and quantitative analysis, BPR of government's purchasing and bidding is eventually implemented. By an instance, the application of this method is introduced.