Abstract: General design formula in seismic combination can be obtained by associating combination of actions based on stochastic processes with design value method.It aims at improving flexibility of design.Due to the large variability of seismic action, the sensitivity factors recommended by international standard are not suitable.If the variability of variables changed greatly, in order to improve the control precision of reliability, standardized sensitivity factor values must be re-valued.Enumeration optimization method is lack of purpose.A function that can give a qualitative optimization direction is proposed.It can give the contribution to the difference between calculated and target value of reliability index caused by the sensitivity factor value of each variable.The function can be used in choosing initial value process and optimizing process, overall optimal result can be obtained under all proportion pairs.The standardized sensitivity factors are used for different design working life and different target reliability index, the errors show that optimization link can use 50-year design working life and a suitable target reliability index.