Algorithm NONEPI and its improved algorithm NONEPI to find non-overlapped frequent episodes exist some defects such as high complexity and "over computing",etc.In this paper, support based on minimal and non-overlapped occurrence is definited ,presents an algorithm called PST_NONEPI for mining frequent episodes based on the prefix shared tree, the algorithm uses a depth-first search strategy,compress frequent episodes have been found to the prefix shared tree, to discover all frequent episodes by maintaining the prefix shared tree.the algorithm only needs to scan the event sequences once,which improves the efficiency of mining frequent episodes. Experiments show that, PST_NONEPI algorithm can effectively mine frequent episodes.