The invention provides a formwork supporting structure for a box beam inclined web and a supporting method of the structure. The formwork supporting structure comprises a formwork supporting rack, a counter-force beam, a counter-force beam fixing device, formwork systems and a supporting system. The counter-force beam is fixed to the formwork supporting rack through the counter-force beam fixing device, the extension direction of the counter-force beam is identical to the length direction of a box beam baseplate, the bottom of the counter-force beam and the box beam baseplate are located on asame plane, the counter-force beam fixing device comprises an oppositely-pulling rebar and a horizontal supporting rod, and the oppositely-pulling rebar provides supporting counter force for the counter-force beam; the formwork systems are arranged at the two sides of a box beam body; the supporting system comprises a supporting steel pipe, an adjustable U-shaped support and a U-shaped base, and the supporting steel pipe aslant supports and is connected with the counter-force beam and the formwork systems. Compared with a traditional formwork supporting method for the box beam inclined web, the method has the advantages that the structure is firm and reliable, the method is convenient to use, the oppositely-pulling rebar can still be recycled, the cost can be lowered, and the efficiency can be improved.