The method of vorticity analysis for axial flow cooling fan optimization is studied. A mathematical physics relationship is established between the circumferential vorticity and aerodynamic performances of fan. And the average circumferential vorticity on the fan blade and the static pressure are positive correlated. Based on a true axial flow fan, the method of vorticity analysis is described in detail. A simulation model of fan pipeline is set up, and an idea of the fan optimization is pointed out by the method of vorticity analysis. The research results show that the negative circumferential vorticity is cut off by the guide rib, which designed on the blade surfaces according to the distribution of the negative vorticity, and the average circumferential vorticity value is improved. The guide rib is designed reasonably using the analysis method, such as the shape, height and thickness of the rib. The aerodynamic performance is improved obviously after adding the guide rib. The test is preceded after the optimization. The test results states that the method of vorticity analysis can be used for the optimization of axial flow cooling fan.