Abstract: The framework of advocacy coalition provides a general paradigm of long-term policy change， but it lacks a deep explanation for the medium and short-term “public perception” mutation of public emergencies. It is argued that public emergencies have a great impact on the external system and policy subsystem of the framework， and lead to the unconventional “public perception” mutation in the short term， resulting in the interruption and separation of the policy subsystem， the unconventional reorganization of new alliance members and the sudden change of dominant alliance， the unconventional consideration of policy formulation and the mutation of policy expectation. Taking the unconventional changes in the demolition and construction policy of provincial expressway boundary toll stations in China as an example， three stages of unconventional policy changes caused by public emergencies are deduced， including “the occurrence and intervention of public emergencies”， “the formation of new belief alliance” and “policy adjustment and restoration of conventional changes”. Moreover， the unconventional policy change model of “public perception” mutation is put forward.

Key words: public perception; unconventional policy change; public emergency; advocacy coalition