Spin-offs are generally considered to have inherent legitimacy advantages due to their genetic characteristics. However， practice showed that many spin-offs were born from the failed business of the parent enterprises， so they have faced the challenge of organizational legitimacy. Through the comparative study of two cases， it finds that in the context of the failure of the parent company’s business， spin-offs face the dual threshold of legitimacy derived from fission activities and entrepreneurial activities. Spin-offs can choose two different organizational identity change paths to obtain cognitive legitimacy and social and political legitimacy in order to cross the threshold of legitimacy. It deepens the research on the legalization strategy of spin-offs， and has important enlightening significance for spin off activities in the context of the failure of the parent company’s business.