The paper gives a comparative analysis of retrieval function among PubMed, Google Scholar and Scims mainly form the following aspects: retrieval methods, retrieval results and output formats. Effects of retrieval are compared through 10 retrieval tests, and respective characteristics of three retrieval tools are analyzed. Google Scholar has the largest scope;PubMed has better retrieval function than the other two;in the aspect of result output, three retrieval tools have their own characteristics.