The invention relates to a treatment method of landfill leachate. Pretreatment is performed through anaerobic treatment, aerobic treatment and a membrane bioreactor, and organic pollution ingredients which are easy to biodegrade are sufficiently degraded at a lower cost; deep degradation treatment is performed through a photoelectric Fenton reaction, and pollution ingredients which are difficult to biodegrade are sufficiently and quickly degraded; hydrogen peroxide is continuously produced through a gas diffusion electrode so as to maintain the Fenton reaction; the production efficiency of the hydrogen peroxide is improved by using 2-ethyl-anthraquinone as a catalyst; the regeneration of ferrous ions is ensured by using ultraviolet rays for illumination, and the Fenton reaction is circularly performed. The medicament cost is reduced, sludge containing iron is hardly produced, a membrane separation technology is not used in a final treatment link, organic waste is efficiently degraded and discharged, a concentrated solution cannot be produced, and the cost is far lower than that by using a membrane separation technology.