Abstract: Design value method based on probability is a new one for structural reliability design proposed in international standard． Compared with current partial factors method，it possesses better flexibility and generality， representing the development of reliability design method． However，the values of their standard sensitive coefficients which are operative and determine the control precision of reliability were set by experiences at all，leading to rather conservative design results． According to the theoretical expressions of basic variables design values，the optimal sensitive coefficients and reliability control mode were analyzed and determined by use of analytic method，and the unified standard sensitive coefficients applicable to either safety and serviceability design were put forwards，which improved evidently the control precision of reliability，and could determine clearly the scope of relative error of reliability index，laying a foundation for setting the practice design value method based on probability．