Abstract: Longitudinal piezoelectric constant is one of the key parameters of piezoelectric materials. The quasi-static method is most widely used to measure this constant. There are often differences in measurement results obtained using commercial instruments. A quasi-static measurement system was established with a dynamic force sensor, traceable to the primary standard. Factors affecting measurement were systematically studied, including the pretension force, the dynamic force, and the electrode shape. In order to obtain stable measurement results of the piezoelectric constant, the static force should be more than 10 N and the dynamic force no less than 0.1 N. Relatively more accurate measurement results of the piezoelectric constant were obtained using an electrode with a smaller spherical radius to clamp the piezoelectric material. Calibration of commercial longitudinal piezoelectric measuring instruments is discussed. The parameters to be calibrated should include the dynamic force, the static force, and the measurement error.