The invention relates to a mobile robot mechanism, in particular to an inspection robot mechanism for a series compensation device. The inspection robot mechanism for the series compensation device is designed on the basis of the differential type principle, and comprises a car body, a first rack, driving mechanisms, rotating reset mechanisms and walking wheels. Each driving mechanism comprises a motor and a differential mechanism, and each rotating reset mechanism comprises a spring, a groove and a cam. The first rack is hinged to the car body. The motors are installed on the first rack. The walking wheels located on the two sides of the car body are driven by the differential mechanisms to achieve rectilinear motion or corner turning motion. The grooves are formed in the first rack. One end of each spring is connected with the corresponding cam which is always located inside the corresponding groove, and the other end of each spring is connected with the car body. According to the inspection robot mechanism for the series compensation device, the front end and the rear end of the car body are provided with the driving mechanisms and the rotating reset mechanisms respectively, the driving mechanisms drive the walking wheels through the differential mechanisms to achieve the rectilinear motion or the corner turning motion, and meanwhile the inspection robot mechanism has the reset function and has better motion characteristics.