Disclosed is a ramp-platform device for an on-board relocatable small vehicle inspection system. The ramp-platform device includes a connection frame having a rectangular shape and defining therein an inner space, first and second intermediate parts which are disposed in parallel with each other and at two opposite sides of the connection frame, first to fourth ramp parts having a substantially triangle shaped longitudinal section. The first and second ramp parts are removably connected to the two opposite ends of the first intermediate part separately, and the third and fourth ramp parts are removably connected to the two opposite ends of the second intermediate part separately. The height of a top end of the first to the fourth ramp parts is substantially equal to the height of the first and second intermediate parts. When it is not in use, the ramp-platform device may be placed on the scanning vehicle of the moving device in a disassembling and folding conditions, and when it is under inspection, the vehicle to be inspected is raised to a predetermined height by assembling and spreading the ramp-platform device, so that a chassis and wheels of the small vehicle may be entered into the scanning range to achieve the inspection of each part of the small vehicle.