The invention relates to a fast conversion dry latrine for civil defense and underground emergency relief engineering and a construction method thereof. The dry latrine comprises a building envelope with one side having an inlet/outlet, three-proofing cloth is adopted as the material of the building envelop, and the building envelop is fixedly connected with a column and/or a beam in an underground garage by a fixed part. According to the invention, the three-proofing cloth is adopted to replace a building block material to make an assembly type civil defense dry latrine which can be quickly assembled in site. Compared with building blocks, the three-proofing cloth is low in price, convenient to construct and light in material, and can be formed in a large area once. Conversion of the civil defense dry latrine does not need professionals, and therefore, personnel labor hour can be saved.