The protection against islanding is an essential function of connectedgrid system, islanding detection can be divided into three categories of the grid side, the external switches of capacitance and the inverter side, and the methods of inverter side also contains two kinds of active and passive. This paper describes the mechanism for islanding and the reason of nondetection zone, on the basis of above, islanding detection methods are classified, introducing the principles of passive and active based on inverter side, and their characteristics and applicable occasions are analyzed. Finally, the detection methods based on different standards in different countries are presented. The results of the study show that every method has its advantages and disadvantages, in actual application, an active detection and a passive detection method should be used in combination at least, in order to obtain better detection effect.