Fast development of photonic integration has promoted researches on grating couplers. Asymmetrical gratings can realize high-efficiency coupling because they break the symmetrical coupling conditions. Slanted gratings， blazed gratings， binary blazed gratings， and others have obtained important development， especially their structural design， manufacturing methods， and test methods have obtained improvement. The working principles and main features for various gratings as couplers between optical fibers and waveguides are introduced. The main types and the main problems and solution methods faced by each type of gratings are systematically analyzed， and some remarkable research results are enumerated. The aim is to help researchers know about the research status and potential development directions， and thus provide some reference for the future related researches.