In the past few years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO). We present a review of current research on the optical properties of ZnO. The wide range of useful properties displayed by ZnO has been recognized for a long time. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including two light-emitting tubes, transparent thin-film transistors, laser diodes that operate in the blue and ultraviolet region of the spectrum, and ultraviolet detector. Optically pumped lasing has been reported in ZnO platelets, ZnO thin films, and clusters consisting of ZnO nanocrystals and ZnO nanowires. Up to now, a number of synthetic methods including electrospinning, hydrothermal, sol-hydrothermal, chemical vapor deposition, spin coating and electrochemical deposition have been used to prepare ZnO nanomaterials such as nanofibers, nanowires, nanorods and so on. The growth and properties of ZnO nanostructures have been extensively studied, but the photoluminescence mechanism in the visible range has seldom been summarized. The photoluminescence spectra can reflect some important information such as surface defects and oxygen vacancies, surface states, photo-induced charge carrier separation and recombination processes in nano-sized semiconductor materials. The optical emission of ZnO is equally complex, with a variety of defect emission states whose structural origins remain controversial. A detailed discussion of photoluminescence, in the visible spectral range, is provided. In this review, we provided a detailed overview on the luminescence mechanism of ZnO nanostructures in the visible range. The review detail exhibits the following four mechanisms of the optical properties of ZnO in the visible range: the influence of the quantum confinement effect, the band edge modulation that has effect of photoluminescence, the influence of surface modification, and the control of defects’ concentration.