Currently， there are some drawbacks such as missing fallibility extremum of fault quantity， heavy workload and low level of automation setting when electro-magnetic transient simulation is used to calculate direct current（DC） protective settings. Aiming at eliminating the impact of those drawbacks on rationality of setting value， a definition of setting preparative parameter of DC protection is proposed. And the influence on it is analyzed from system operation mode and fault time， then a method how to obtain it is put forward. Furthermore， the setting flow chart for DC protection setting calculation with simulation is designed， and all setting preparative parameters for whole DC protective devices are included. Simulation results show that the method can reasonably reduce labor for setting calculation without miss limit values as well. And the setting of DC protective device with the proposed setting calculation flow chart can reduce the setting workload and raise the setting automation level greatly. The study can enhance the rationality of setting value and it is in favor of making the setting work of DC protection more normatively and systematically.