The invention relates to a displacement measuring device and a velocity measuring method of a drilling traction robot. The measuring device comprises a support bar, a stopper, a hydraulic, a piston of the hydraulic, a displacement sensor, a seal baffle, a waveguide, a magnetic ring, and a magnetic ring support plate. The invention can realize instant measurement and instant feedback of the velocity of the drilling traction robot and can provide data reference for automatic drilling of the drilling traction robot.