According to the National Contract Law, when determining Estimation cost Contract officers should consider contract quantity, contract period, supply and demand condition, difficulty of contract enforcement, terms and condition, and other various conditions based market price, costing based pricing, and appraisal. And they should not overestimate or underestimate the estimation cost. But the estimation cost system is used as preparedness for audit against the contract law. In this study, we identified the factors affecting estimation cost and analyzed their influence on estimation cost.