The invention relates to the technical field of main variable foundations, in particular to an assembling type main variable foundation provided for solving the problems that an existing main variable foundation is inconvenient to construct, long in period and poor in quality. The main variable foundation is divided into two components to be prefabricated in the factory, field mounting is achieved, construction efficiency is improved, construction quality is ensured, and the project cost is reduced. According to the adopted scheme, a bottom plate is integrally molded through a mold directly in a factory, a bending beam is integrally molded through a mold directly in the factory, the lower end of the bending beam is provided with a first inserting part and a second inserting part which extend downwards, a first sliding groove and a second sliding groove allowing the first inserting part and the second inserting part to be inserted in are formed in the bottom plate, the inserting parts at the lower end of the bending beam slide in the corresponding sliding grooves in the length direction of the sliding grooves, the inserting parts of the bending beam are inserted into the sliding grooves of the bottom plate, after the positions are adjusted, binding materials are poured in, and the inserting parts and the sliding grooves are connected in a fastened manner.