Abstract: The traditional methods to measure the electrode displacement in resistance spot welding include direct measurement method, measurement of upper electrode movement, and measurement of long arm tooling. The deformation of welding tongs was analyzed by finite element method(FEM) under the load of electrode force and dynamic electrode force. And the deformation influence on measurement method of upper electrode movement and measurement method of long arm tooling was analyzed. It is concluded that the lower electrode has relative larger vertical displacement and deflection angle for dynamic electrode force, so the electrode displacement cannot be measured correctly using measurement method of upper electrode movement and measurement method of long arm tooling. At last, the method to measure electrode displacement was proposedbased on trapezoidal relationship.