The invention provides a mounting construction method of a steel structure support seat, comprising the following steps of: (1) piling and laying computer modules of a support seat and confirming the connection positions of reinforcing steel bars and the support seat; (2) preliminarily reserving bar-penetrating holes in the corresponding positions of the support seat; (3) mounting the support seat in the appointed positions; and (4) arranging and connecting the reinforcing steel bars and penetrating the reinforcing steel bars into the bar-penetrating holes. The invention can greatly lower the construction difficulty of the support seat and saves the construction cost.