The torsional effect of a rectangular piezoelectric quartz is studied in the article. Using the anisotropic elasticity and Maxwell electromagnetic theory, the stress field and electrostatic field is founded, and then by the Finite Element Method the distribution of the electric field in the piezoelectric body is obtained. Based on theoretical analysis of the bound charge distribution, the measuring electrodes are effectively disposed on the surfaces of the piezoelectric wafers. The theoretical and experimental results show that the measurement charge is linear with the torque. The research will provide the basis for the torque measuring technique.