A hybrid nanomechanical resonator system consisting of a diamond nitrogen vacancy (NV) color center and a cantilever beam is proposed, where the NV color center is embedded at the bottom of the cantilever beam, and the coupling is achieved through the interaction between the stress generated by the vibration deformation of the cantilever beam and the spin electrons in the diamond NV color center. Then, the coherent optical properties of the hybrid system are investigated using optical pump-probe technique. Firstly, an all-optical approach for measuring the frequency of nanomechanical resonator is proposed based on the absorption spectra of the hybrid system. Under the condition of the red sideband, the coupling strength between spin and nanomechanical oscillator can be determined by observing the splitting width of two peaks in the absorption spectra. In addition, due to the extended coherence period of the electron spin in NV center, an all-optical mass sensing approach at room-temperature is further proposed based on this hybrid system.