Water diffusion in hydrogels significantly affects their mechanical behavior. The existing experimental studies on the fracture behavior of hydrogels affected by water diffusion mainly focused on macroscopic crack observations. The experimental characterization of crack tip deformation fields in aqueous environments remained unexplored. Furthermore, theoretical analysis of water diffusion effects on crack tip deformation lacks validation across different loading conditions. In this study, utilizing a custom-built mechano-chemical coupled tensile platform and digital image correlation (DIC) method, we investigated the effects of water diffusion on crack tip deformation in polyacrylamide (PAAm) hydrogels under constant force and constant displacement. Experimental results revealed a non-equilibrium diffusion competition mechanism at the crack tip under different loading conditions. Finite element simulation based on the equilibrium theory coupling large deformation with water diffusion was performed to analyze the swelling ratio near crack tips under constant force. The simulation results confirmed that stress-induced chemical potential gradients drive water accumulation at crack tips. Further, comparative experiments in oil and aqueous environments were performed to compare the time scale of water diffusion within the hydrogel and the time scale of water diffusion between the hydrogel and the surroundings. It is found that the load applied to the crack tip leads to a decline of chemical potential around the crack tip. The difference of chemical potential drives the water diffusion from the surroundings to the crack tip. This experimental result validates the existing theoretical analysis. The experimental result also demonstrates that water exchange between hydrogels and their surroundings instead of the water migration within the hydrogel itself dominates the crack tip deformation evolution. The elucidated mechanism of crack-tip diffusion and environmental interaction hold significant potential for guiding the design of hydrogels with enhanced fracture resistance and tailored mechanical performance in demanding applications such as biomedical implants and soft robotics operating in aqueous settings.