In this paper, the model of the maximum utility of profit margin of commercial banks under the credit risk and the interest risk is reformulated with full consideration of the profile of the losses of bad debts for the commercial banks. The influence of the requirement in the capital adequacy by the central bank to the commercial banks on bank's yields is studied.Analysis shows that considering the risk loss and risk cost of the commercial bank,enhancing the capital adequacy to commercial bank will increase margin profit of commercial bank with decreasing absolute risk avoidance under the Ross concep.