Abstract: Epidermal growth factor receptor tyrosine kinase inhibitor（EGFR TKI） is the first-line treatment for non-small cell lung cancer, but it is difficult to avoid drug resistance during the therapy. A variety of TKI resistance mechanisms have been discovered, including EGFR T790 M mutation, HER2 amplification, MET amplification and trans-differentiation, as well as 15%～20% of patients with unknown mechanisms of TKI resistance. In this study, we developed a method to resolve drug resistance mechanism of molecularly targeted therapy in lung adenocarcinoma patients based on liquid biopsy and high-throughput sequencing. We collected pleural effusion samples before the TKI therapy and after development of TKI resistance in a lung adenocarcinoma patient by liquid biopsy,followed by enrichment of tumor cells and high-throughput sequencing of whole exome and transcriptome. The sequencing results were analyzed to discover genomic and transcriptomic alternations after drug resistance for deciphering the resistance mechanism that paved the way for optimizing therapy.