The torsional stiffness check of the shaft is the calculated amount of torsional deformation of the shaft during operation, which is measured by the torsional angle per meter of shaft length. The torsional deformation of the shaft will affect the performance and working accuracy of the machine. For example, if the torsional angle of the camshaft of the internal combustion engine is too large, it will affect the correct opening and closing time of the valve; The torsional angle of the transmission shaft of the gantry crane's motion mechanism will affect the synchronization of the driving wheels; It is necessary to have large torsional stiffness for the shaft that is in danger of torsional vibration and the shaft in the control system.