Raman spectroscopy provides vibration and rotation modes of the molecule, and directly reflects the molecular structure of the analyte. Surface enhanced Raman spectroscopy may be applied to practical applications because greater Raman scattering cross section. This paper proposed a large-area nanoslit array Surface Enhanced Raman Scattering (SERS) substrate which is cost effective. By exciting two resonance modes and coupling them together simultaneously, a strong local electromagnetic field was obtained. Up to 108 Raman signals enhancement factor was achieved. Down to 10-15 M minimum detection concentration was achieved. This substrate can be used as surface plasmonic resonance (SPR). Super-high electromagnetic field enhancement effect also can improve the sensitivity of SPR detection.