Aiming at the demand of automatic drilling of cylindrical workpiece surface such as ammunition shell,a design method of automatic drilling system of gantry robot was proposed based on laser measurement technology.The laser displacement measurement technology was used to realize the on-line monitoring and calculation of the workpiece axial reference joint surface,the axial position of the prefabricated hole center,the circumscribed position of the prefabricated hole center,to realize the automatic identification of the drilling target position.A servo motor was used to drive the three-coordinate truss manipulator to realize the full coverage of the drilling position in the length direction and the circumference direction of the workpiece,and the PID control algorithm was used to realize the precise control of the drilling depth.The test results show that the drilling system runs stably,the standard deviation of the center position of the prefabricated hole reaches 0.02 mm,and the precision of the drilling depth reaches 0.15 mm.The drilling quality is improved,the man-machine isolation of the drilling process of the ammunition shell is realized,the system can meet the actual production demand.