Objective To study the clinical significance of EGFR mutation in patients with advanced non -small cell lung cancer combined with malignant pleural effusion,and to provide reliable theoretical basis for clinical treatment .Methods 3 0 patients of advanced non -small -cell lung cancer complicated with malignant pleural effusion in Zhoushan island area were selected.DNA was extracted in the pleural effusion and EGFR 19,21 two loci of gene mutation was detected by sequencing PCR.EGFR and clinical characteristics of the patients (gender,age,smoking history,disease types of cases and in the level of CEA level)was compared.Results Among the 30 cases,4 cases of gene mutation,1 case of male patient,3 cases of female patients,4 cases of adenocarcinoma,4 cases of non smokers, 2 cases of EGFR19 deletion,2 cases of EGFR21 mutation.Among them,3 patients were treated by biological target therapy,the survival time was more than 1 year,and there were no obvious adverse reactions,and the effective rate was 75.00%.Conclusion The gene mutations of EGFR were detected in the patients with advanced non -small cell lung cancer combined with malignant pleural effusion,and the mutation rate 13.30%,which was high in female,non smoker and adenocarcinoma,and it could be used to treat the tumor.