The application of variable cross-section type stirring paddle in 50 kt / a WPA plant reactor in Compound Fertilizer Plant of Shaanxi Shanhua Fertilizer Co.,Ltd are introduced.Through the contrast analysis between variable cross-section type stirring paddle in the process of single tank and single stirring paddle and turbine type stirring paddle in the process of single tank and multiple stirring paddle,the design capabilities,running features and running effect of variable cross-section type stirring paddle are evaluated.