Optical micro/nanofibers are one-dimensional free-standing waveguiding structures with diameters close to or smaller than the vacuum wavelength of the guided light. Fabricated by physically drawing glass fiber at high temperature, these fibers show excellent surface smoothness and diameter uniformity, high mechanical strength, tight optical confinement, strong evanescent field, evident surface field enhancement, and large wavelength/diameter-dependent waveguide dispersion, especially much lower waveguiding loss than all other micro/nanowaveguides with similar geometries. These merits offer them great potentials in applications ranging from near-field optical coupling, optical sensing, atom optics, nonlinear optics, laser technology,and optomechanics. In this review, starting from the basic waveguiding properties of optical micro/nanofibers, we introduce our recent progress in high-precision fiber fabrication and micro/nanofiber-based near-field coupling, optical sensors,and nonlinear optical devices. At same time, we also mention relative works from other groups. Finally, we conclude this article with a brief outlook.