A tunable hard X-ray source from intense laser interacting with overdense solid targets is proposed. It is shown that the incident angle of the laser plays an important role in influencing the radiation quality, including the spectrum of the radiation, the energy conversion efficiency from laser to radiation, and the angular distribution of the radiation. The two dimensional relativistic particle-in-cell simulations shows that, to get the highest energy conversion efficiency, the optimal incident angle for the present simulation parameters is 30°, and the energy conversion efficiency from laser to radiation in the optimal incident angle is about 5%, which is far more efficient than other incidence condition using the same laser pulse. The intensity of the laser used in the simulation is 1.34×1022 W/cm2. Detailed analysis shows that the vacuum heating radiation mechanism is the dominant mechanism responsible for hard X-ray emission, and the radiation frequency spectrum is tunable when the incident angle changes.