Objective To compare the advanced non -small cell lung cancer (NSCLC)patients before and after chemotherapy peripheral blood EGFR mutation status,we understand whether the chemotherapy drug impacts the EGFR mutation status of the advanced NSCLC patients,so as to improve the precision of EGFR TKIs -drug use. Methods To collect the peripheral blood of 30 cases of advanced NSCLC before chemotherapy and after chemotherapy for 6 cycles.DHPLC technique was used to detect the EGFR mutation states of EGFR exon 19 and in exon 21.Results In 30 patients,chemotherapy prior EGFR mutation positive rate was 53.3% (16 /30).After 6 cycles of chemotherapy, the EGFR mutation positive rate was 36.6% (11 /30),the consistent rate was 56.6 (17 /30)before and after chemo-therapy,inconsistent rate was 53.4% (13 /30).10 cases from positive to negative before chemotherapy,3 cases from negative into positive before chemotherapy with statistical significance (P =0.046).Six EGFR19 exons changed, change rate of 20%,8 EGFR21 exons shift changed at a rate of 26%.EGFR19,21 shift in 1 case,with no statistical significance(P =0.39,P >0.05).Conclusion (1)The late NSCLC patients before and after peripheral blood of EGFR mutation status change,so before starting the targeted therapy we must recive real -time detection of peripheral blood EGFR mutation status,so as to decide whether to choose EGFR TKIs targeted drug therapy.(2)EGFR21 exons transformation rate is higher than EGFR19 exons conversion rate,but with no statistical difference,this phenomenon may be related to EGFR19 exons patients who with EGFR mutations -TKIs treatment efficiency is higher.