The invention provides a qualitative and quantitive isothermal detection method of RNA (Ribonucleic Acid). The method comprises the steps of after cutting RNA at fixed points by dnazyme (DNAzyme), amplifying RNA through a strand displacement isothermal amplification technique (SDA); and carrying out qualitative or quantitive detection by inspecting a reporter group G-tetramer released from an SDA product. The method can measure trace RNA (comprising mRNA and miRNA) quickly, simply, conveniently, highly sensitively and specifically, and meanwhile, the risk of pollution is reduced.