<p>The seismic performance of frame joints is one of the key issues in the application of prefabricated concrete structures. To investigate the seismic performance of prefabricated concrete frame joints assembled by new mechanical connection steel bars, low reversed cyclic loading tests and numerical simulations were conducted in this paper. The study investigates the effects of mechanical connection steel bar and types of core zone post-cast concrete (ordinary concrete (OC), high performance concrete-Engineered Cementitious Composites (ECC) and Ultra-High Performance Concrete (UHPC)) on the hysteretic behavior, bearing capacity, energy dissipation capacity, and stiffness of prefabricated concrete frame joints. The findings indicate that, compared with specimen with core-zone post-casted OC, specimen with core-zone post-casted UHPC exhibits an increase in bearing capacity, energy dissipation capacity, and initial stiffness by 22.7%, 36.3%, and 24.2%, respectively. Specimen with core-zone post-casted ECC show no significant change in load-bearing capacity or initial stiffness, but energy dissipation capacity improves by 31.3%. The enhancement effect of specimen with core zone post-casted UHPC is more effective than that of specimen with ECC. Increasing the reinforcement ratio and reducing the shear span ratio can effectively improve the specimens’ bearing capacity and initial stiffness, while increasing the beam section height has a limited effect. The restoring force model for prefabricated concrete frame joints assembled by mechanical connection steel bars was developed. The predicted results agree well with the tests, confirming the model’s validity. This study offers technical references for applying prefabricated concrete frame joints with mechanical connection steel bars.</p>