Abstract: In solid-state laser, the processing technology of laser crystal has an important impact on the total quality of the output laser. For the defects of the deviation of the center position of spherical end face from the central axis in round rod crystal, a method for testing the center position of spherical end face was put forward. Through theoretical calculation of the transmission matrix in the optical path and solving the changes in position and angle of the reflection light, the relationship between deviation of the center position from the central axis and the distance from the spot position to the hole of the aperture was obtained. In experiment the distance from the spot position to the hole of the aperture was measured when the testing laser was debugged to the different positions on the plane surface of the crystal. And the deviation of the center position of the spherical end-face on the central axis of the crystal was calculated at last. The center positions of spherical end face were tested for two different kinds of crystals. The vertical distances of the center position of spherical to the central axis for two -3 crystals are 2.55 mm and 1.1 mm, and 3.25 mm and 0.9 mm for two -4 crystals. Moreover, the possible cause of the error was analyzed.