System torsional rigidity is an important design index, having important influence on operating performance of the advanced actuator; therefore, this paper emphasizes the study on calculation of system torsional rigidity. This paper firstly introduces working principle and structural features of the novel ball screw transmission. Then uses commercial CAD and FEM softwares, SolidWorks and Cosmos/Works, fulfils deformation analytical computation for such three key parts as driveshaft, fixed guiding sleeve and straight-rotary sleeve. Next, sum up each term of torsional rigidity. Finally, makes a conclusion that the system torsional rigidity of the advanced actuator satisfies the designing demand.