The invention relates to an inner wall grinding device used for a long and fine round pipe. The device comprises a fixed mounting base placed on the ground and used for mounting of the round pipe, a shaft mounting base placed on the ground and located at the left end of the fixed mounting base, a mounting table placed on the ground and located at the right end of the fixed mounting base and a motor fixed to the mounting table; an end grinding wheel is connected to the shaft mounting base, the motor is connected with a starting grinding wheel, multiple grinding wheels are connected between the starting grinding wheel and the end grinding wheel, L-shaped clamping blocks and arc clamping grooves matched with the L-shaped clamping blocks are arranged on the grinding wheels, a first shaft and an L-shaped clamping block are arranged on the starting grinding wheel, and a second shaft and an arc clamping groove are arranged on the end grinding wheel. The grinding device has the beneficial effects that the grinding wheel assembling manner is adopted, the inner walls of long and fine round pipes with different lengths can be ground, the higher flexibility and higher compatibility are achieved, use and taking processes are convenient, the whole device is small in size, and the space utilization rate of a factory plant can be improved.