The invention relates to a method and a kit for extracting RNA and application of RNA. The method comprises the following steps: (S1) centrifuging a biological sample to obtain supernate (S2) adding an exosome precipitation solution into the supernate, and carrying out uniform mixing and centrifugation, so as to obtain exosome precipitates (S3) adding a total RNA extraction reagent and isometric alcohol into the exosome precipitates, acutely mixing, and adding the mixture into an adsorption column (S4) centrifuging the adsorption column, adding RNA pre-washing liquid, RNA cleaning buffer liquid and deionized water, and carrying out repeated flushing and centrifugation, so as to obtain total RNA. The invention further relates to application of fused RNA and other tumor-specific RNA extracted from exosome of body fluid in aspects of early diagnosis, screening and diagnosis of tumors. Fused RNA and other tumor-specific RNA are extracted from the exosome and are applied to the early diagnosis and screening of malignant tumors such as esophagus cancer and breast cancer, thereby simply realizing the cancer liquid diagnosis with the characteristics of little wound, good patient compliance and convenience in collection and storage.
