Based on the simulating operation practice of East China electricity market， this paper constructs an evaluating system for the purchasers' bidding strategy. It puts forward three classes of indices， i.e. status， strategy and effect， to reflect the economic characteristics of the purchaser's bidding. This evaluating system can provide a valuable reference for the power grid company， and the guide for the bidder to make right decisions. Through calculating the historic data， this paper also analyzes the influence of transmission constraints on the market participants and the evaluation method.