Abstract: In the present "Building Code Requirements for Reinforced Concrete Structures (TJ10-74) and the revised edition (GBJ10-89) which is going to be issued in the near future, the formulae of calculating short period stiffness are in great approximation because of the analytic model and the empirical results under the single test loading condition. In this paper, based on the new unified formula of calculating the short period stiffness of reinforced-prestressed concrete beams under any kind of loading condition, the calculating analysis for the stiffness of flexural members under the several loading conditions have been processed.