The utility model relates to an adjustable formwork support device, including two channel -section steels, four square steel tubes, a plurality of connection square steel tube, bolt, its characterized in that: every channel -section steel on be equipped with the spout, be equipped with a plurality of holes on the spout, four square steel tubes also open slottedly, and the one end inslot opens at least and has a hole, and grooved square steel tube can freely slide in the spout of channel -section steel, every channel -section steel both ends are placed a grooved square steel tube respectively and are fixed integrative with the bolt through corresponding the hole, square steel tube transverse connection are connected together through many to two channel -section steels, connection square steel tube of every channel -section steel both ends difference vertical welding. The utility model discloses but wide application in the door and window entrance to a cave, especially highly higher door and window entrance to a cave construction adopts this device can ensure the stability of formwork, does not take place the membrane that expands, and a form removal board is simple and convenient simultaneously, and it is many to have enough to meet the need the number of times. The utility model discloses easy and simple to handle, safety, practicality, can be used widely.