As a typical form of emergency language service, the emergency prevention and control slogans (EPCS) play an important role in the prevention and control of social emergencies in China. However, due to the characteristics of "emergency", the prevention and control slogans are errorprone, which can cause a negative impact on the language ecology. Based on the theory of linguistic ecology, this paper conducts a thorough analysis of the error-prone slogans during the COVID-19 epidemic in China. First, error-prone slogans can be divided into four categories from the internal language ecological environment: language standardization errors, application appropriateness errors, content adaptability errors, and ethical compliance errors. Second, this paper assesses three aspects of error-prone slogans from external social ecological environment: the degree of errors, the distribution of errors, and the citizens' normative willingness. Finally, the paper puts forward suggestions to prevent language conflict, stop language exclusion, eliminate language dissent and govern the language environment in order to reduce error-prone emergency prevention and control slogans, improve the quality of emergency language services, and build a harmonious ecological environment inside and outside the language.