Proton exchange membrane fuel cells (PEMFCs) with high-power density and large-scale design are primary for superior cell performance, low cost and adequate power supply. However, understanding the internal non-uniformities in commercial-size PEMFCs (> 250 cm²) through in-situ measurements is challenging. Modeling has emerged as an effective tool for predicting non-uniform transport phenomena, but previous studies have been limited to single-channel or small-scale models (< 100 cm²) due to the complex geometry and instability of commercial-size PEMFCs. Moreover, appropriate coolant flow parameters in commercial-size PEMFCs need to be further analyzed to balance the water-thermal states. In this study, a three-dimensional multi-phase non-isothermal PEMFC model was extended to the commercial scale, including metallic plate structure, dot matrix, coolant channel and membrane electrode assembly. The influences of inlet coolant velocity and temperature on water-thermal management of the commercial-size PEMFC were comprehensively investigated. The results indicated the dominated factor affecting current density shifts from membrane dehydration to oxygen starvation along the air flow. The severe local hotspot was observed in the corners of the coolant outlet, which is attributed to the low coolant flow velocity in the both-side channels. Increasing both the inlet coolant flow velocity and decreasing the inlet temperature mitigated the local hotspot, with slightly sacrificing the membrane hydration near the inlet region, but the overall water content and uniformity are improved obviously. Lower inlet temperature resulted in less vapor amount, leading to a higher oxygen concentration, which significantly improve the local low current density at the downstream area. The cooling strategy of decreasing inlet coolant temperature was found to be more effective than that of increasing coolant velocity, and an inlet temperature of 343.15 K keeps the average membrane temperature near the 353.45 K with excellent temperature uniformity. This work can shed light on the thermal management characteristics, design and optimization of the commercial-size PEMFCs.