On the basis of research the structure of the speed control type inpipe robot, using the technology of computer fluid dynamics (CFD) for analyzing the flow field of the drive speed control unit of the robot, the different pressure field and velocity field were gotten under the drive speed control unit in different working condition. The influence was analyzed of the change of cone valve opening degree in drive speed control unit on moving velocity of the robot. The result shows that the flow velocity of the valve port gradually becomes smaller with the increase of the opening degree of the cone valve, and the vortex is generated on both sides of the axis of the pipeline because of the space in the downstream of the valve port becomes larger. The pressure which is in the high pressure zone changes not obviously, and the pressure which is in the subhigh pressure zone is gradually reduced，while the pressure which is in the negative pressure zone rises slightly. The pressure in the downstream area of the cone valve gradually increases, and the pressure difference that is between the two ends of the driving speed control unit gradually reduces.