Abstract: The ocular bioavailability of traditional ophthalmic preparations is relatively low, and it is difficult to have a satisfactory therapeutic effect on ocular diseases, which is mainly due to the difficulty of traditional ophthalmic preparations to pass through many physiological barriers in the eye and the short residence time of the preparations in the eye. In order to improve the ocular bioavailability of drugs and reduce the adverse drug reaction to ocular tissues, some novel drug delivery systems, such as nanoparticles, microspheres, and in situ gels, have been employed to develop ophthalmic preparations, and have attracted increasing attention of researchers. In terms of the rapid development of ocular drug delivery systems, recent advances in ocular drug delivery systems are summarized in this paper. Firstly, ocular structure and physiological barriers which restrict drugs into the eye are introduced. Secondly, novel ocular drug delivery systems, including nanoparticles, liposomes, lipid nanoparticles, microspheres, and in situ gels are introduced. Finally, the future prospects and crucial problems of ocular drug delivery systems in clinical treatment are focused on.