The invention relates to a method for treating marsh gas and marsh liquid by an electrolyte. The method comprises the following steps: (1) introducing the marsh gas to be purified into an oxidizing agent-containing electrolyte for washing, wherein the oxidizing agent comprises sodium hypochlorite and hydrogen peroxide, and the pH of the electrolyte is 6.5 to 7.5; (2) collecting and storing the marsh gas which is treated in the step (1) to obtain the purified marsh gas; (3) refluxing the electrolyte which washes the marsh gas, filtering, and recycling elemental sulphur; (4) treating the marsh liquid by using waste electrolyte, and enabling the waste electrolyte and the marsh liquid to react according to the volume ratio of 1:8 to 10, wherein the reacting time is 40 to 60 minutes. The marsh gas and the marsh liquid are treated by adopting the method provided by the invention, the removal rate of the hydrogen sulphide from the marsh gas is up to 99 percent or above; the marsh liquid is disinfected; the removal rate of COD from the marsh liquid reaches 80 percent or above; the BOD removal rate reaches 85 percent; the ammonium-nitrogen removal rate reaches 92 percent; the marsh liquid which is treated by the method can be directly discharged.