A prefabricated thermal insulation integrated grid template structure was proposed for a concrete high arch dam project in severe cold region. The structure not only cooperates with the cast-in-place arch dam, but also provides thermal insulation throughout its entire lifespan. The crack distribution, bearing capacity, and deformation of the formwork under out-of-plane load were studied using the combination of experimental and numerical simulation methods. The test results show that the cracks of the formwork, which is subjected by the action of out-of-plane load structure are mainly distributed at the center of the bottom beam span, the beam-column interface and the center of the grid plate under. Vertical deformation at the center of the loading plate is significantly greater than that at the beam span. When the load reaches 600 kN, the slope of the deformation-load curve decreases. When the load reaches 1 100 kN, the steel bar at the beam end yields. Under the pressure equivalent to 100 m of water depth, the out-of-plane deformation of the specimen is less than the yield deformation. Cracks appear on the tensile side of the beam and plate, but no significant damage occurs on the compressive side. The research results provide a foundation for the application of prefabricated thermal insulation integrated formwork in high arch dam structure in severe cold area.