Capital structure of company changes company value in a frictional market environment through cutting down cost and decreasing moral risk and causal problem in trust agency. The authors apply method of asymmetric information game to analyze how to make design of mechanism on the basis of existing revenue and cost of bankruptcy, make the company's manager maximize shareholder's wealth through maximizing own effectiveness, thus define the best radio of liabilities.The authors show that good companies have higher value than difference one in a assured mechanism, afitness capital structure could reduce the problem in trust agency of company's manager,higher risk project can bering more value for compay.