A theoretical scheme to enhance the sum sideband generation (SSG) via double radiation pressure is proposed. In this scheme, both sides of the double-cavity system are driven by red and blue detuned pump lasers and frequency components are generated at the sum sideband through optomechanical nonlinear interaction. The results show that the efficiency of SSG can be improved with orders of magnitude. We further investigate the properties of SSG in resolved and unresolved sideband regimes. The efficiencies of upper sum sideband generation (USSG) and lower sum sideband generation (LSSG) are the equivalent in the unresolved sideband regime when the threshold condition is satisfied. It is worth noting that with the increase of the ratio between the dissipation rate of the cavity field and the decay rate of the mechanical resonator (MR), the amplitude of the LSSG can be superior to that of the USSG. Our scheme may provide a potential application in realizing the measurement of high-precision weak forces and quantum-sensitive sensing.