Biological research requires dynamic and wide-field optical microscopy with nanoscale resolution to study the biological process. To address this issue, a structured illumination microscopy based on near-field diffraction enhancement using metallic grating is proposed. The technique introduces spatial light modulator and metal grating on the basis of the conventional e-pi microscope. The sub-wavelength imaging performance of this technique is studied theoretically and numerically. The results show that the transverse spatial resolution of full width at half maximum is 65 nm at wavelength of 520 nm and numerical aperture of 1.3. Compared with the traditional wide-field microscopy, the resolution of the technology increases by about 3.7 times. This technology has potential application in biological research.