The utility model provides a formwork device for pour at floor entrance to a cave, when aims at overcoming reserving the floor entrance to a cave and carry out the concrete placement shutoff small -size construction among the prior art, there not be unified, convenient support system, expend the manual work, quality control is unstable, still possesses dangerous shortcoming, provides a formwork device for pour at floor entrance to a cave, includes roof and bracing piece, top surface of the top plate be equipped with the anti -leakage sheet rubber, the roof lower surface is equipped with downwardly extending's jack, the internal diameter size of jack is corresponding with the outer diameter of bracing piece one end, the bracing piece be the structure of adjustable length, bracing piece one end and jack grafting. The utility model discloses having saved the time, having reduced artifical input, supported effects is good, and circulated used repeatedly is fit for using when pour at the floor entrance to a cave.