Most of existing in-pipe robots are applied to defect inspection and regular maintenance, etc. There is almost no in-pipe robot for big-diameter pipelines cleaning and are still problems of traction force and obstacle-overcoming. To deal with the problems, a novel wheeled and wall-pressing type in-pipe cleaning robot (IPCR) with high pressure water jet is proposed. Then the preload mechanism, traction force, and obstacle-overcoming capability of the IPCR are analyzed. The vibration equations of the simplified vibration system of the IPCR are established. Also, the necessity of preloading force is verified and methods to improve obstacle-overcoming capability are proposed. Finally, the traveling capability is verified in a dynamics simulation system. The simulation results show that the proposed IPCR is powerful with traction force and has a certain capability of obstacle-overcoming. Setting the attitude angle is zero and adding preloading force to all springs can obviously weaken vibration of the IPCR.