Metal　halide　perovskites　with　broad　optical　absorption　and　long　carrier　lifetime　are　considered　as　ideal　photocatalysts.　However,　their　poor　stability　in　water　greatly　impedes　their　application　in　photocatalytic　H-2　evolution　because　they　lose　their　crystalline　structure　in　water.　Herein,　we　proclaim　a　new　class　of　photocatalysts:　all-inorganic　Cs-Cu-Cl　perovskite　quantum　dots　(QDs).　It　exhibits　a　high　photocatalytic　hydrogen　production　rate　of　similar　to　3.1　mmol/g/h　without　any　cocatalyst　under　AM　1.5-G　solar　irradiation　(100　mW/cm(2)).　Especially,　it　remains　the　high　activity　for　up　to　330　h　without　apparent　deterioration　of　the　hydrogen　production　rate.　Density　functional　theory　(DFT)　calculations　reveal　that　the　Cu　site　works　as　the　electron　and　proton　absorption　sites　as　the　H-2　production　active　center.　To　our　best　knowledge,　there　is　no　report　of　metal　halide　perovskites　as　water-stable　photocatalysts.　This　work　opens　an　innovative　way　for　guiding　the　exploration　of　metal　halide　perovskites　photocatalysts　for　stable　photocatalytic　H-2　evolution.