This study presented the experimental and theoretical results of insulated concrete Sandwich panels with innovative dumbbell-shaped steel fiber-reinforced polymer (FRP) composite bar (SFCB) connectors under flexural load. The influences of FRP thickness and raised thickness of dumbbell ends of connectors, axial compression ratio, the content of vitrified microspheres in the wythes, and loading direction were discussed. The increase in thickness of a glass FRP (GFRP) jacket on the hybrid bar from 2 to 3 mm led to increased initial cracking load, ultimate load, and flexural stiffness of the Sandwich panels by 75, 49, and 16%, respectively. The increase in the thickness of dumbbell ends from 4 to 6 mm led to increased initial cracking load, ultimate load, and flexural stiffness of the Sandwich panels of 18, 46, and 9%, respectively. The incorporation of vitrified microspheres in concrete wythes resulted in a significant increase in the load-carrying capacity of Sandwich panels but decreased ductility. Increased axial compression ratio from 0/1 to 0.2/1 contributed in improving the crack resistance and ultimate loads of Sandwich panels. Further increase of the axial compression ratio to 0.4/1 led to crushing failure of concrete wythe ends. Specimens under negative loads had higher ultimate loads than the counterparts under positive loads. Three-dimensional finite-element (FE) models were developed to simulate Sandwich panel flexural behavior and numerical results compared with the test data. Then, the verified FE model was used to analyze the influence of the arrangement of dumbbell-shaped SFCB connectors. Increased connector spacing from 550 to 650 mm was found to have an insignificant influence on load-deflection responses. Moreover, analytical solutions for deflection of Sandwich panels under combined axial-flexural load were obtained, in which the effect of slipping between the facade and structural wythes and shear deflection were considered. The predicted deflection at the ultimate load agreed well with the test results. This study provided a theoretical basis and design reference for FRP-jacketed steel-composite connectors in applications of Sandwich wall panels with large insulation layer thickness.