Fabricated steel structure building system and construction method

The invention belongs to the technical field of assembly type buildings, particularly relates to an assembly type steel structure building system and a construction method, and aims to solve the problems that an existing traditional steel structure is very troublesome to disassemble after being used, and most of disassembled steel pipes cannot be restored to the original shape, the following scheme is provided: the assembly type steel structure building system comprises a horizontal rod and a vertical rod, a matching groove is formed in the bottom end of the horizontal rod, and a matching block matched with the matching groove is fixedly connected to the top end of the vertical rod; the positioning assembly is arranged between the matching groove and the matching block and is used for primarily positioning the horizontal rod and the vertical rod; the fixing mechanism is arranged in the horizontal rod and used for fixedly connecting the vertical rod with the horizontal rod; the supporting mechanism is arranged