The invention relates to an illuminator used in a fiber-optical evanescent field. Part of one end of the fiber optic is ground to be an inclined surface, and the inclined surface goes beyond the position of the fiber core 1 to 10 micron; when entering from the fiber core, the light is reflected to the end surface of the fiber optical in the position of the inclined surface, and a total internal reflection is generated on the end face of the fiber optical. By adopting the technology of combination of the optical fiber and the internal reflection imaging principle, the illuminator used in the evanescent field for biological illumination is fabricateed on a single optical fiber. Compared with the prior illuminator used in the evanescent field, the design of the invention has the advantages of simple structure, smaller volume, more flexible and stable light path. Therefore, a multifaceted illumination on the surface of the bioanalyte can be achieved, and a major breakthrough is made in the performence of the illuminator used in the evanescent field. A novel fluorescent micro-imaging system is convenneintly formed by adopting the technology of combination of the microscope, meanwhile, the illuminator is easily combined with other imaging technique and probing technique and has a wide application range.