How to improve the photocatalytic efficiency of photocatalysts is an eternal theme in the field of catalysis. In this study, we have systematically explored the mechanism of noble metal doping (Rh, Pd, Pt, Ag and Au) to enhance the photocatalytic performance monolayer GeSe by first principles study. Se-rich growth conditions facilitate noble metal atom substitution into GeSe. Substitution doping with Rh, Pd and Pt as well as Ag and Au adsorption on the photocatalyst surface will introduce impurity levels in the band gap of GeSe. Moreover, all noble metal (especially Rh) doping can make GeSe respond to the entire solar spectrum. More importantly, Rh-doped GeSe may be the most excellent photocatalyst due to its high sunlight utilization, low photogenerated carrier recombination rate, numerous catalytic active sites and strong oxidizing photogenerated holes.