Abstract: With the wide access of renewable generator to power grid, the stability of renewable generator equipment access to power grid has been widely concerned with the risk of small-signal instability issue. Impedance method is effective for stability analysis, and obtaining accurate impedance characteristics of renewable generator is the key to impedance stability analysis. As a method to obtain impedance characteristics by injecting small signal perturbation, impedance measurement has become a hot topic in the field of grid-connected stability of renewable generator. In impedance measurement, it is necessary to inject perturbation signal to excite the system to respond, and calculate the impedance according to the response. In order to meet the accuracy requirement and rapidity of impedance measurement, a variety of perturbation signal types were proposed. This paper listed the types of perturbation signals which were widely studied, and discussed their application characteristics from two aspects of measurement accuracy and efficiency. Then, the applicability of various perturbation signals in various application scenarios was compared, and the selection methods of perturbation signal types in different application scenarios were given.