Disclosed is an apparatus and method for synchronously treating sewage and sludge through a step-feed partial nitrification coupling anaerobic ammonia oxidation process, belonging to the biological treatment field. Ammonia rich landfill leachate is firstly pumped into an aerobic reactor to realize partial nitrification process; exogenous surplus sludge coupling with partial nitrification reactor effluent are input to an anoxic reactor together for achieving integrated fermentation and denitrification process; finally, effluent from the anoxic reactor is pumped into an integrated autotrophic nitrogen removal reactor by a step-feed mode, the integrated reactor contains two main running units of aeration and anoxic stirring, ammonia is oxidized into nitrite in aeration stage, and the generated nitrite and ammonia contained in secondary influent are further removed through anammox process which operates stably and reliably, realizes efficient nitrogen removal from landfill leachate without external carbon source addition, and realizes the purpose of exogenous excess sludge reduction simultaneously.