Abstract: The long glass fiber reinforced polypropylene fluid-assisted injection molding pipes were molded by four processes: Gas-assisted injection molding process (GAIM), gas-projectile-assisted injection molding process (G-PAIM), water-assisted injection molding process (WAIM) and water-projectile-assisted injection molding process (W-PAIM). The effects of each process on the wall thickness, glass fiber fracture length and glass fiber orientation of the pipes were compared and studied. The results show that the wall thickness of the W-PAIM process pipes is the thinnest and most uniform, and the wall thickness of the GAIM process pipes is the thickest and most non-uniform. G-PAIM had better wall thickness uniformity than WAIM pipes, but WAIM pipes has thinner wall thicknesses. The glass fiber fracture lengths are unevenly distributed among the four process methods. The average glass fiber fracture length is ranked as WAIM>GAIM>W-PAIM>G-PAIM. The introduction of the projectile intensifies the glass fiber fracture effect, so that the glass fiber fracture length is shorter. In G-PAIM, WAIM and W-PAIM processes, the orientation of glass fibers along the flow direction tends to increase gradually from near the mold wall layer to the middle layer to near the runner layer, and the orientation of GAIM glass fibers is disorganized. The degree of glass fiber orientation of each process pipes is ranked as W-PAIM>WAIM>G-PAIM>GAIM.