Although transition-metal oxides offer the potential for intimate coupling of energy storage application and environmental sustainability, how to find the suitable relationship between materials structures and properties is still a problem to explore further applications. In this work, Jahn-Teller effects proved by Crystal Field Theory (CFT) and Density Functional Theory (DFT) are used to predict the electronic structures of MoO3 and MoO2 reasonably, such results guided us to design two more reasonable applications. On account of the metallicity tendency of MoO2 with a stronger electron mobility from band structure, MoO2/rGO/g-C3N4 composite was performed as a high-performance electrode in asymmetric supercapacitors (SCs). MoO2 with the assistance of mesoporous graphitic carbon nitride and high conductivity graphene shows an enhanced capacity at 1700 F g−1 at 1 A g−1 and cycling retention at 84% retention after 3000 cycles for supercapacitors, the corresponding assemble asymmetric devices shows a maximum power density of 6.25 kW kg−1 at an energy density of 16.0 W h kg−1. Furthermore, the proper band structure of MoO3 predicted by DFT calculation has guided MoO3/rGO composite as a photocatalyst to degrade tetracycline, which shows a high elimination efficiency of 90.6% within 2 h illumination of simulated solar light.