Optical microscopy performs an increasingly important role in clinical diagnosis and basic scientific research. With the development of novel fluorescence probes, light controllers, and detectors, super-resolution optical microscopy breaks through the diffraction limit and provides new tools for modern biomedical research. Among these techniques, structured illumination microscope (SIM) achieves super-resolution by using spatially coded structured illumination which down modulates spatial frequencies beyond the cutoff into the pass band of the microscope. SIM shows lower photo bleaching and phototoxicity, higher imaging speed, and no special requirements for fluorescent probes, which has significant advantages in application to live-cell biomedical research. In this paper, the important principles and technological progress during the development of SIM are firstly reviewed. Then we focus on the key experimental techniques and difficulties in hardware design and image reconstruction of SIM. Finally, the several applications in biological imaging are listed. It is expected that this review can provide guidance for designing and using SIM.