A new kind of osciiiations caused by waveiength stabiiization feedback ioop is investigated.The resuits of 1D numericai simuiations confirm the moduiations of the eiectron energy and FEL power, and the caicuiated moduiation freguency and depth are in good agreement with the experiments.It is found that the freguency creep caused by superradiance usuaiiy resuits in this kind of iimit-cycie-iike osciiiations.