Abstract: To evaluate the seismic performance of the concrete frame in which precast beams and columns are connected by post-tensioned tendons, numerical analysis of four beam-to-column assemblages which were tested under cyclic reversal loads was carried out using the software DRAIN-2DX. Then the simplified calculation formula of the beam end bending moment at several key points on the force-drift relation curve (including the cracking point, the linear limit point, the yielding point and the ultimate limit point) is derived based on principle of statically balancing. The analysis results indicate that the calculated shear force-drift hysteretic loops and the envelope curve agrees well with the experimental results, and the key points on the envelope curve are close to the experimental ones, while the analytical initial stiffness is relatively higher; the formula is proved to be effective and convenient for engineering application.