Abstract: Includes the following steps: (1) Mix organs and tissues with formamide and monovalent cation salt solution, homogenize them to obtain the dehydrated biological sample; (2) Mix the dehydrated biological sample with monovalent cation salt solution for incubation; (3) Add the monovalent cation salt solution with precipitation effect to the mixture, mix them and centrifuge, then pour the supernatant into another centrifuge tube; (4) Add isopropanol, mix it and centrifuge, and then discard the upper phase liquid, the lower phase liquid and the visible residual impurities between the upper and lower phases to get white RNA precipitate. This method proposed in the invention enables efficient isolation of protein from RNA in the biological samples.