The invention relates to a manganese oxide-graphite phase carbon nitride composite photocatalytic material and a preparation method thereof. The manganese oxide-graphite phase carbon nitride composite photocatalytic material is prepared by depositing manganese oxide nanoparticles on the surface of layered graphite phase carbon nitride, and the manganese element loading capacity of manganese oxide in the composite photocatalytic material is 0.3-1.2 mol%; manganese dioxide or trimanganese tetroxide or dimanganese trioxide or a mixed oxide of manganese dioxide, trimanganese tetroxide and dimanganese trioxide is adopted as manganese oxide. Manganese oxide in the composite photocatalytic material is uniformly loaded on graphite phase carbon nitride, the loading capacity is controllable, the good catalytic capacity is achieved, a manganese oxide cocatalyst is closely combined with graphite phase carbon nitride, therefore, the defects that a single photocatalyst is high in photoproduced electron hole pair composite ratio and low in photocatalytic efficiency are effectively overcome, the solar utilization efficiency is greatly improved, and the excellent catalytic activity is achieved when the composite photocatalytic material is used for photocatalytic hydrogen production. The composite photocatalytic material has the wide application prospect in the fields of photocatalysis, electrochemistry, energy, environments and the like.