The invention provides a water treatment method for removing trihalomethane in drinking water by utilizing UV (ultraviolet)/H2O2. The water treatment method comprises the following steps: introducing the drinking water into a reaction device, starting a magnetic stirrer in the reaction device, and adjusting the rotational speed of the magnetic stirrer to be 125-300 r/min; putting a UV lamp tube capable of stably emitting light into the reaction device, and arranging a quartz sleeve tube outside the UV lamp tube; adding H2O2 into the drinking water in the reaction device for treatment, wherein the additive amount of H2O2 is 5-30 mmol/L, the power of a UV lamp is 12-75 W, and the retention time is 20-60 minutes; removing trichloromethane, tribromethane, dibromochloromethane and bromodichloromethane contained in trihalomethane in the treated drinking water, wherein the removal rates of trichloromethane, tribromethane, dibromochloromethane and bromodichloromethane can reach 43.97%, 99.61%, 99.38% and 93.07% respectively. The water treatment method has the benefits that the method is capable of completely decomposing trihalomethane, free of secondary pollution, low in H2O2 consumption and low in energy consumption, has a certain removal effect on TOC (total organic carbon) and UV254 in the drinking water, and has a very good removal effect on trihalomethane.