The accuracy of computer numerical control（CNC）machine tools has been one of the important factors of restricting the machining quality of machine tools.In the process of assembling and using the CNC machine tools, it is an important part of accuracy debugging and fault diagnosis of CNC machine tools. Among them, the rotary workbench of machine tools accuracy will directly affect the machining quality. A practical solutionwas provided to the failure of a rotary workbenchof vertical lathe based on type 12TC16090. Reference is provided for solving similar failure of machine tools. 