A formwork early-removal construction method allowing the three-dimensional space size to be adjustable comprises the following steps that S1 an early-removal supporting system is installed; S2 formworks are removed; S3 a main beam (4) is removed. The early-removal supporting system comprises a formwork part (16), a secondary beam part (17), a main beam part (18), a hollow screw double-adjustment knocking-down type early-removal supporting head part (19), an independent supporting part (20) and a tripod part (21). According to the formwork early-removal construction method, the one-time input number of the formworks can be greatly reduced, the arrangement number of the formworks is reduced by 1/3-1/2, service lives of the formworks and service life of the supporting system can be prolonged, construction costs are saved by more than 20%, the construction period is effectively shortened, construction speed is increased, and work efficiency is improved by more than30%.