Top arch joints are critical in the bearing capacity of prefabricated structures. The mechanical properties of the top arch joint are investigated by analyzing the mechanical behavior of top arch joints with large bending moments during the construction period based on longterm insitu monitoring data in the Changchun metro prefabricated station. Variation trends of joint stress, relative deformation, and relative rotation angle varying with the construction progress of the top arch are discussed. Finally, the performance of top arch joints in different construction stages is analyzed and compared with numerical calculation results. The results show the following. (1) At the beginning of the top components′ assembly into a ring, the structure has a selfadaptive period and the joint stress and deformation are large. (2) After soil backfilling and waterlevel recovery, the joint′s axial force increases, and the joint′s stress and deformation decrease, positively affecting the joint′s bearing capacity. (3) The joint stress′s overall variation range is small. The two tenons of doubletenon joints rely on each other′s occlusal action to bear the external force and reflect the different properties (one pulling and one pressing) during the construction. After completing all construction stages, the doubletenon joints stabilize in a compressive stress state. (4) The top arch joint′s overall deformation is small and the safety margin is rich. The research results have practical guiding significance for prefabricated metro stations′ joint and structure design.