Using short-glass-fiber-reinforced polypropylene (SGF/PP) as the experimental material, circular tubular parts were fabricated by four processes, namely overflow-based water-assisted injection molding (WAIM-O), short-shot water-assisted injection molding (WAIM-S), overflow-based water-penetrated floating-core-assisted injection molding (WPAIM-O), and short-shot water-penetrated floating-core-assisted injection molding (WPAIM-S). Wall-thickness measurement, scanning electron microscopy (SEM) characterization and pressure-resistance tests were performed to systematically investigate how manufacturing processes affect the residual wall thickness, glass-fiber orientation and pressure-bearing performance of tubular parts, and clarify the correlation mechanism between macroscopic properties and microstructures. The results demonstrate that the introduction of a floating?core greatly improves the penetration stability of melt during water?assisted injection molding. Products made by the overflow method possess larger residual wall thickness than those from the short?shot method, and samples prepared via the WPAIM process have thinner residual walls compared with WAIM counterparts. Among the four forming methods, WPAIM-O yields parts with the best wall?thickness uniformity whereas WAIM-S delivers the worst-uniform walls. SEM observations reveal that glass fibers in WAIM-O samples are randomly distributed, while fibers from the other three processes are predominantly aligned along the melt-flow direction. The pressure-resistance testing proves that the wall-thickness level, thickness uniformity and fiber orientation collectively govern the pressure-bearing capacity. Specimens produced by WAIM-O achieve the optimum pressure-resistance property of 7.3?MPa, distinctly surpassing WPAIM-O (5.1?MPa), WPAIM-S (4.0?MPa) and WAIM-S (3.3?MPa). It is concluded that higher wall?thickness, better thickness uniformity and increased randomness of glass-fiber orientation collectively lead to superior pressure-resistance performance of final parts.