The invention discloses a belt mounting assisting device for an internal combustion type generator set. The belt mounting assisting device comprises an upper mounting shell and a lower mounting shell,and distance adjusting gear racks are mounted in the upper mounting shell and the lower mounting shell. The distance adjusting gear racks are rotationally connected through a distance adjusting gear,and a locking buckle is arranged on the distance adjusting gear. Rotary motors are fixed into the upper mounting shell and the lower mounting shell, and rotary cams are fixed to output shafts of therotary motors. Jack catches and locating columns are arranged on the sides, away from the rotary motors, of the rotary cams, totally four jack catches are arranged, and the jack catches are evenly arranged around the locating columns. According to the belt mounting assisting device, the upper mounting shell, the lower mounting shell, the distance adjusting gear, an arc-shaped top plate, an arc-shaped supporting plate and the rotary cams are arranged, so that the problems that use cost is high, the structure is complicated, use is inconvenient, the belt mounting assisting device is not suitablefor assembly line work, and maintenance cost is high are solved.