The invention discloses a method and a device for detecting gene mutation and expression quantity. The method comprises the following steps: S1, extracting RNA, interrupting, and carrying out reversetranscription to obtain cDNA; S2, constructing a gene library by adopting cDNA; S3, capturing and enriching a target gene from the gene library by utilizing specific hybridization of a capture probe and the target region; S4, sequencing by using a high-throughput sequencer to obtain RNA targeted sequencing data; S5, analyzing changes of gene mutation and expression quantity in the RNA targeted sequencing data, wherein the step S5 specifically comprises the following substeps: S51, analyzing the gene expression quantity; S52, analyzing gene overexpression; S53, carrying out gene fusion analysis; S54, carrying out the fusion mutation expression quantity analysis; S55, carrying out the single nucleotide variation analysis; S56, analyzing the expression quantity of the mononucleotide variationmutation. RNA transcripts expressed by tumor-related genes can be efficiently enriched, and the expression quantity and mutation conditions of the tumor genes in tumor tissues are analyzed.