Clean and renewable photocatalytic technology for methane reforming into high-value liquid fuels, such as methanol, is a promising strategy for commercial industrial applications. However, poor charge separation, sluggish methane activation, and excessive oxidation collectively inhibit the production of methanol from photocatalytic methane reforming. Herein, we have developed enhanced metal-support interactions between a GaN nanowire photocatalyst and a Cu nanoparticle (CuNP) cocatalyst via p-doping in GaN. CuNP-loaded p-type GaN (Cu/p-GaN) with enhanced metal-support interaction has 3.5-fold higher activity (12.8 mmol g-1 h-1, higher than previous reports) for methanol production in photothermal catalytic methane reforming with oxygen as an oxidant and sunlight as the sole energy source than CuNP-loaded intrinsic GaN (Cu/i-GaN) or n-type GaN (Cu/n-GaN). In-situ IR measurements indicate that enhanced metal-support interaction significantly promotes activation of methane and formation of methanol. Combining with X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) simulations demonstrate that this enhanced metal-support interaction in Cu/p-GaN greatly improves electron transfer from p-GaN photocatalysts to the 3d states of CuNP cocatalysts through the interface between them. Catalytic pathway simulations further reveal that the enhanced metal-support interaction in Cu/p-GaN also desirably decreases the reaction energy of rate-determining methanol desorption, which decreases the excessive oxidation of the produced methanol and accelerates the regeneration of surface catalytic sites. These studies and findings offer critical insights into the design and development of metal nanoparticle-loaded photocatalysts for photocatalysis-based methane reforming into methanol.