The utility model discloses an adjustable mechanism for lifting a hydraulic support from the bottom. The adjustable mechanism comprises a base bridging device and a jack connecting base, wherein a chute is arranged at the front end or the rear end of the base bridging device, so that the jack connecting base can be arranged in the chute in a sliding manner; lateral lugs are respectively arranged in the corresponding positions on two sides of the jack connecting base; a pressure plate comprises a left pressure plate and a right pressure plate pressed against the positions of the lateral lugs on the two sides of the jack connecting base and matched with the positions of the lateral lugs, so as to locate the jack connecting base; and the jack for lifting the hydraulic support from the bottom can be installed at different heights by controlling different installation manners of the pressure plate, more particularly, the jack for lifting the hydraulic support has two installation heights, i.e., heights for use and transportation. Since the jack for lifting the hydraulic support from the bottom can be installed at different heights according to the requirements, the adjustable mechanism of the utility model can meet the requirements of heights for the lowest structure of the support.