The stress of pier-beam connections of Ⅰ-shaped steel-concrete composite rigid frame bridges is complex， the force transmission mechanism and load distribution of pier-beam joints are still unclear， and the calculation method of pier-beam joints is lacking. By comparing the test results of the pier-beam joints of theⅠ-shaped composite rigid frame bridges， the verified solid finite element calculation model is adopted. According to the stress state of each component of the pier-beam joint under the action of the axial force， bending moment and shearing force of the pier， the force transmission mechanism and load bearing ratio of the pier-beam joint are analyzed. The design calculation method of each component is established， and the trial design of the Ⅰ-shaped composite rigid frame bridge is carried out. The results show that the force transmission mechanism and path of axial force and bending moment are similar， and the shearing force transmission mechanism is different. The longitudinal beam and the transverse beam bear 45%~55% of the load transfer， respectively. Under the action of axial pressure and axial tension， the load transfer path and the load bearing proportion of the longitudinal beam change. The load directly transmitted by the longitudinal beam is mainly transmitted through the lower flange of the longitudinal beam， and the load transmitted to the transverse beam is mainly borne by the studs of the web. The design of the longitudinal beam should consider the additional stress of the pier load. The transverse beam is calculated according to the uniform load force mode of the simply supported beam. The design of the transverse beam web connector is calculated according to the load transferred to the transverse beam. The studs of the longitudinal beam web and lower flange are arranged by structural requirements. The pier-beam joint of trial design bridges meets the requirements. The finite element calculation results are consistent with the theoretical calculation results. The established pier-beam joint design method can be applied to the design of Ⅰ-shaped composite rigid frame bridges.