CsxWO3 nanorods can be used to sensitize the single layer g-C3N4, where full spectrum light harvesting excited electrons to drive the photocatalytic reduction of N-2 into NH3. Under UV light, both water splitting and solar ammonia synthesis reaction exhibit high activity. However, selectivity towards ammonia over hydrogen is realized under NIR irradiation. With the control of methanol, O-2 can directly decide the NH3 or H-2 evolution on photocatalyst. The origin is the strong capture of O-2 with the electrons from the photocatalyst under light irradiation to yield the oxygen active species, which transfer electrons subsequently with help of methanol to generate NH3. However, H-2 production will be suppressed by O-2. And with its sacrifice, methanol preserves the produced NH3 from oxidation. The O-2-sacrificial agent mediated NH3 evolution reaction found here provides insights in the promotion role of them in other catalysis.