In the simulation of Software Defined Network (SDN), the existing network simulation tools usually do not consider the processing delay of SDN switchs. To make the simulation result more realistic and accurate, a scheme to simulate the processing delay was proposed. First, the scheme divided the process of the switch forwarding into two aspects: inquiry operations on flow table and execution of various actions, and then transferred the two aspects into processing delay by using processor frequency and memory cycle. Measurement and comparison were conducted on the processing delay of switches with different configuration in real and simulation environments. The results show that the simulated processing delay of the proposed method is almost close to that in real environment, it can accurately estimate the processing delay of switches.