The invention discloses a square-to-round roll forging blank manufacturing method of an overall bulging extrusion drive axle housing. The problems that in hollow piece roll forging blank manufacturing, the pipe wall is thickened, and the wall thickness is not uniform are solved. The method comprises the steps of 1, blanking; 2, heating; 3, roll forging blank manufacturing, wherein two passes of roll forging forming and one pass of shaping roll forging are carried out on a roll forging machine through a mandrel, wherein (1) in the first pass of roll forging forming, a forging roll of the roll forging machine rotates by a circle to complete the first pass of roll forging forming of the right end of a pipe blank (5), a square pipe is subjected to roll forging to form an oval-section pipe, meanwhile, the pipe blank (5) and the mandrel (6) are separated, (2) the oval-section pipe is subjected to roll forging to form a round pipe in the second pass of roll forging forming, (3) shaping roll forging is carried out, and (4) the pipe blank (5) subjected to shaping roll forging is rotated by 180 degrees, the right end of the pipe blank (5) is clamped by a clamp, and the unformed left end, clamped by a jaw at the beginning, of the pipe blank (5) is formed in a roll forging manner through the same method; 4, air cooling; 5, straightening; and 6, fixed-size cutting of the two ends.