The invention relates to a main structure of a combined type house and an assembly method thereof. The main structure is a rectangular case serving as a main load-bearing part of the whole combined type house. The main structure comprises an outer wall which surrounds the rectangular outside and plays a role in bearing, internal partition walls which partition the space enclosed by the outer wallinto a plurality of spaces, and a bottom board of which the inside is provided with a pipeline structure; besides, part of fixtures are prearranged in each partitioned space, the pipeline structure comprises main water supply and drainage, heating and electric pipelines which are in matched connection with the fixtures and are processed integrally in a factory. The main structure can be put in aninternational standard container with the length of 12 meters for integral transportation. After arriving at an actual assembly destination, the main structure is only integrally hoisted to a preset concrete base of the assembly destination and is connected with the local pipelines to finish the assembly, so that the construction period is greatly shortened.