Compared to the traditional open surgery, minimally invasive abdominal surgery results in improved results. In order to further reduce the number of incisions, some people put forward laparoendoscopic single-site surgery (LESS) which can get better results. But it also has several disadvantages, such as the tools` interference with each other, the restriction of tools` motion space due to incision. The tools which are able to work in the abdominal cavity entirely can overcome the disadvantages mentioned above, they are ideal for the LESS. We are working on a kind of in vivo robot unit which works entirely in the abdominal cavity. It has the function of lighting and visual feedback. For the purpose of providing better surgical field, the robot unit can tilt to a certain angle and clean the lens automatically. This paper focuses on introducing the design procedure of key transmission parts, self-cleaning executive mechanism and shells.