The invention relates to the technical field of machining, in particular to a long roll machining support device matched with a large-sized machine tool for use. The long roll machining support device comprises a substrate which is vertically arranged on a machine tool bottom plate and can slide in the horizontal direction of the machine tool bottom plate in a reciprocating mode; the substrate is provided with a support seat reciprocating along the vertical direction of the substrate; a pair of rotatable rollers are arranged on the support seat; pressure sensors are arranged at the surfaces of the pressure rollers; the substrate is provided with a driving mechanism which is used for driving the support seat to move in the vertical direction and a controller which receives signals of the pressure sensors and controls the driving mechanism to work. A long roller can be properly supported by adjusting the heights of the rollers according to needs, so the middle of the long roll is not bent and the machining precision is ensured.