A new piezoelectric torsional actuator with the structure of spiral electrode based on the interdigital electrode (IDE) was designed, and the theoretical equation of strain for points in the effective electrode region of spiral electrode plane is derived and established. The theoretical equation was verified through the analysis software ABAQUS, and the influences of voltage, radial dimension and disk thickness on the strain of the piezoelectric actuator were studied. The results show that the piezoelectric torsional actuator with spiral electrode can produce large tangential strain and radial strain output, increasing the voltage and reducing the radial size and thickness of the piezoelectric disc are beneficial to improve the driving performance of the actuator. The tangential strain of the piezoelectric torsional actuator with spiral electrode can reach 17.5 times and the radial strain is 1.6 times that of the common electrode when the spiral angle, the radial size of the piezoelectric disc and the voltage are fixed.