A boom-adjustable horizontal hydraulic jack with a pull-lock mechanism belongs to a lifting apparatus. The jack comprises a chassis, a hydraulic assembly, a press handle, a boom assembly, and a link rod assembly, wherein, the boom assembly comprises a bearer, a forearm, and a rear arm; the link rod assembly comprises a first link rod and a second link rod; wherein, a pull-lock mechanism is additionally arranged on the bearer, and comprises a guide rod seat, a guide rod, a pull handle, a guide sleeve, a steel rope, a dialing plate shaft, and a locking pin shaft.