The invention discloses a mounting method of a prefabricated building, comprising the following steps: base level treatment, binding of basic steel bars, mounting of first level vertical members, pouring of basic concrete, mounting of first level top horizontal members, pouring of concrete, mounting of second level vertical members, pouring of concrete, mounting of second level horizontal members, pouring of concrete and sequential cyclic operation according to the mounting operation flow. The method disclosed by the invention has the advantages of good integrity of structural connection, good safety and earthquake resistance, good environmental friendliness and energy-saving performance, reliable quality and convenience of quality inspection; the prefabrication rate reaches over 95%; secondary large area pouring, leveling blanket, masonry and other field operation procedures are saved; labor and materials are saved; by virtue of continuous mounting, the efficiency is improved, and the construction period is shortened; precise mounting and one-step positioning can be realized; the safety risk is reduced, and the quality is upgraded; waste water, waste materials, garbage, dust and noise generated by site construction and pollution of transportation to the air environment are reduced; and the prefabricated building is safe, durable, energy-saving, efficient, green, environment-friendly, economical and applicable.