Optical microfibers and nanofibers have diameters close to or smaller than the wavelength of the guided light. Fabricated by physical drawing of glass or polymer materials，these tiny fibers show excellent surface smoothness and diameter uniformity，high mechanical strength，tight optical confinement，strong evanescent field，significant surface field enhancement，and large and abnormal waveguide dispersion，which bestow them with a variety of applications in fields ranging from optical communication，laser technology，sensors，nonlinear optics，and quantum optics. The application of micro-nano fiber in sensor，modulator and laser and the development trend of micro-nano fiber in the future are mainly introduced in this paper.