We present a strong coupled quantum dot-nanomechanical resonator system and investigate its nonlinear optical properties using optical pump-probe technology. The process of evolution of the nonlinear Kerr spectrum is studied for different resonator frequencies under low temperature and room temperature, respectively, and the results indicate that even at room temperature the nonlinear Kerr spectrum can still be resolved. In addition, we further theoretically propose a room temperature nonlinear optical mass sensing scheme based on the hybrid nanoresonator system. When the masses of external nanoparticles (such as biomolecules including baculovirus, coronavirus, DNA, etc.) are attached to the nanomechanical resonator, the resonance frequency shift caused by nanoparticles can be measured by nonlinear Kerr spectrum, and then the mass of nanoparticles can be determined. The hybrid coupled nanoresonator system will have potential applications in ultra-sensitive and high-resolution mass sensors.