The invention relates to an automatic supporting force regulating device for a crankshaft supporting center rack. The device comprises a V-shaped supporting block, an adjusting plate, two connecting bolts and a cylinder connecting block, wherein one ends of the two connecting bolts which are arranged in parallel are fixedly connected with the adjusting plate, and the other ends of the two connecting bolts are fixedly connected with the cylinder connecting block; the rear part of the V-shaped supporting block is provided with a groove; the adjusting plate is movably arranged in the groove of the V-shaped supporting block through two adjusting bolts; dish-shaped springs are sleeved on the adjusting bolts in the groove; the adjusting bolts penetrate through the adjusting plate and the dish-shaped springs so as to be fixedly connected with threaded holes in the V-shaped supporting block in a matching manner; and through regulating the compression amount of the dish-shaped spring at the back end of the V-shaped supporting block, the size of the supporting force can be automatically regulated. The automatic supporting force regulating device is reasonable in structure, simple to manufacture and convenient in use and can automatically regulate the supporting force, thus being an ideal automatic supporting force regulating device for the crankshaft supporting center rack. The automatic supporting force regulating device is used for irregular shaft turning support heel blocks.