Petri网是使用很广泛的用于复杂系统描述的工具。PRM网是一种特殊的Petri网，主要用于并行程序的性能评价和预测，使用PRM网进行预测，通常使用的是程序模拟的方法。本文首先对PRM网作了简要的介绍并做出适当的修正，然后基于修正后的PRM网提出了一种基于计算的性能预测方法。该方法主要可以分成三个步骤：首先根据P网建立一个状态跃迁列表，然后根据资源映射图建立执行图，最后计算执行图中最长路径的长度。对于不同的资源映射图，只需要重做后两步，就可以预测出其运行时间，相对于模拟来说，这种方法要便捷得多。

Petri net is a useful tool for system description in many research areas. PRMnet is a specified Petri net for the performance evaluation and prediction of parallel programs.The commonly used method for prediction with PRMnet is simulation. In this paper we first introduce the PRMnet briefly and then make some modifications.We introduce a method by calculation with the modified PRMnet. There are three phases in this method:first generate a transition list with Pnet;and then generate an execution graph with resource mapping; the length of the longest path of the graph is the total execution time, which can be calculated by some algorithms efficiently. Thus, with different resource mappings, we just need to redo the last two steps, which is much easier than simulation.