PIM-SM is preferred among the current intra-domain multicast routing protocols. But it is not widely deployed in Internet till now. To provide suggestions of improving this protocol, we analyze the performance of it in this paper. The characteristic of our analysis is that we use the SPN model, which is an excellent tool for performance analysis in many areas. Based on the SPN model of PIM-SM we establish for the first time and router realization, we make performance analysis of PIM-SM according to different message types, finding that Register message and Join/Prune message cause most router processing load, while Join/Prune message and Bootstrap message consume most network bandwidth.