The invention discloses a domestic garbage incinerator slag multifunctional water permeable brick and a preparation method thereof, and belongs to the field of solid waste recycling. domestic garbageincinerator slag is subjected to water washing, ball milling and grading pretreatment and then supplemented with aggregates such as blast furnace slag, waste ceramic and sludge ash and additives, andthe multi-layer functional integrated water permeable brick is prepared through layered compression molding. The surface layer of the water permeable brick is a macroporous strength reinforced layer,a middle water permeable and reinforced adsorption layer and a lower microporous reinforced adsorption layer. The obtained multifunctional water permeable brick has different layers and different functions, so that the effect of adsorbing pollutants and heavy metals in permeable water is achieved, and secondary pollution is reduced. The water permeable brick is high in strength, strong in functionality, simple in production method and good in applicability.