Results: EGFR mutations were detected in 97.3% plasma samples; the T790M mutation accounted for 37.3% and is accompanied by a sensitive mutation TKI; The T790M mutations ratio after treatment was higher than before treatment with TKIs (p < 0.001); the median total duration of EGFR-TKI treatment was significantly longer in patients with T790M mutation than in those without (16.8 months vs 12.5 months, p = 0.005); the T790M mutation ratio was higher in patients with a deletion on exon 19 than in L858R mutation on exon 21 (p=0.028), in Erlotinib treatment group higher than in Gefitinib and Afatinib treatment group (51.4% vs with 20.0% and 33.3%, p=0.039).