The simulating model of Josephson junctions in PSpice is constructed and used in the investigation of Shapiro steps.In the condition of little capacitance

we have researched the influence of resistively and capacitively shunted Josephson junction's parameters

including critical current and normal resistance

on Shapiro steps.We found that it can improve the steps by both to reduce the normal resistance under a larger rf-current circumstance and to increase the normal resistance in the condition of a smaller rf-current.We also found that the larger the junction critical current

the higher the Shapiro steps

when the junction resistance keeps constant.The results are of important referential value for the voltage standard and THz signal detection by Josephson junctions.