In order to better understand the mechanism of surface enhanced Raman spectroscopy (SERS) and further improve the Raman enhancement factor, a strategy which combines SERS and mechanical controllable break junctions (MCBJ) is employed. With such a strategy, the gap width between two nanoelectrodes can be adjusted precisely during the period of SERS measurement. The dependence of SERS intensity on the gap width and the incident laser polarization are investigated. Moreover, a nano gate-electrode with adjustable bias voltage is introduced, and the gate electrode effect to the Raman signal intensity is investigated in system. The experimental results demonstrate that the Raman signal intensity critically depends on the biased gate voltage, which provide a new method to enhance the Raman signal and benefit the theory investigation for the Raman enhancement mechanism.