The invention discloses a self-help hoisting mechanism of a low-position cantilever walking type bridge erection machine, comprising a rear outrigger, a front outrigger, a middle outrigger, a main beam with an inverted concave cross section, and a beam hoisting crown block. A left leg and a right leg of the rear outrigger are rigidly connected with a left lower chord and a right lower chord at the two sides of the main beam as well as a web respectively, and the foot part of the rear outrigger is provided with a sliding shoe; a left leg and a right leg of the front outrigger are articulated with the lower chords at the two sides of the front end of the main beam so as to form a stable bent structure on the cross section, and a rectangular frame is formed between the upper half part of thebent and the main beam; the middle outrigger is an opened rectangular frame and the upper transom thereof consists of a plurality of opened supporting bars; a left column and a right column of the middle outrigger and a lower cross beam form a U-shaped steel frame; the supporting bars are formed by length-adjustable bars and the two ends of the supporting bars are respectively connected with a left column and a right column of the U-shaped steel frame by removable plug connectors; and the middle outrigger is supported under a longitudinal guide rail arranged at the bottom surface of the main beam through a supporting roller arranged on the shoulder of the middle outrigger.