This study systematically investigates the phase change transpiration cooling process and heat transfer deterioration mechanisms of 3D printed metal porous media structures under non-uniform heat flux density conditions through an irradiation heating experiment. During the experiment, the low heat flux region maintained a heat flux density of 71 kW·m^-2, while in the high heat flux region, a heat flux density ranged from 84 kW·m^-2 to 108 kW·m^-2. The experimental results indicate that, under the influence of non-uniform heat flux, the high heat flux region is affected by vapor blockage, leading to higher local flow resistance and difficulty in coolant supply. This results in the gradual formation of a surface dry-out zone, with both the structure temperature and the dry-out zone continuously increasing over time. In contrast, in the fully wetted zone of the low heat flux area, the coolant preferentially flows into this zone due to lower flow resistance, forming a dominant channel, which further reduces the temperature of the fully wetted zone. During the experiment, a noticeable inflection point in the temperature rise curve was observed when heat transfer deterioration occurred, where the wall temperature sharply increased after surpassing the inflection point. Due to the presence of the dominant channel, even when the coolant supply mass flow rate is increased after the wall temperature exceeds the inflection point, it becomes difficult to prevent further expansion of the surface dry-out zone and the continuous rise in temperature.