Abstract: This study aims to systematically clarify how the gas-liquid flow patterns at the pump inlet evolve with varying inlet gas volume fraction (IGVF) and how these changes affect the overall pump performance and gas distribution within the impeller. Experiments are conducted under various combinations of IGVF and liquid-phase flow rates to investigate the centrifugal pump’s performance losses and gas-liquid flow regimes over a range of operating conditions. The results show that when the pump operates near the design flow rate, its performance decreases with increasing IGVF. At low flow (Q_l = 0.6Q_lBEP, IGVF = 8%), gas-liquid separation occurs in the inducer region; at high flow (Q_l = 1.4Q_lBEP, IGVF = 13.6%), severe gas-liquid separation develops in the impeller passages. Both scenarios precipitate an abrupt drop in performance. As IGVF increases, the inlet-section flow pattern transitions from bubbly flow I to bubbly flow II, and ultimately evolves into plug flow. When the inlet flow pattern is bubbly flow II or plug flow, agglomerated large bubbles impinge non-uniformly on the inducer blades, producing the greatest performance loss as IGVF increases; by contrast, under bubbly flow I, the degradation is comparatively mild. Increasing the liquid flow rate promotes a more uniform gas-liquid distribution in the inlet pipe and delays the onset of bubbly flow II and plug flow; however, it also accelerates bubble accumulation at the impeller inlet, triggers phase separation within the passages, and thus adversely affects pump performance.