Objective To investigate the effect of the SMAC gene on paclitaxel sensitivity and cellular activity in lung adenocarcinoma cells based on the caspase-3/Bcl-2/Bax signaling pathway. Methods A paclitaxel-resistant cell line A549/Taxol was established for lung adenocarcinoma, and the cells were divided into four following groups: pcDNA-NC (transfected with pcDNA-NC blank vector), pcDNA-SMAC (transfected with pcDNA-SMAC vector), siRNA-NC (transfected with siRNA-NC empty virus vector), and siRNA-SMAC groups (transfected with siRNA-SMAC lentiviral vector). The SMAC mRNA expression in cells was detected by qRT-PCR; cell sensitivity was detected by MTT; cell proliferation ability was detected by cloning assay; cell invasion ability was detected by Transwell; apoptosis ability was detected by flow cytometry assay; and caspase-3, Bcl-2 and Bax protein expression in cells were detected by Western blot analysis. Results The SMAC mRNA expression was significantly lower in A549 cells compared with BEAS-2B cells (P < 0.05). The SMAC mRNA expression was significantly higher in the pcDNA-SMAC group than that in the pcDNA-NC group cells (P < 0.05). The SMAC mRNA expression was significantly lower in the cells of the siRNA-SMAC group (P < 0.05) than that in the siRNA-NC group. The SMAC mRNA expression was significantly lower in the cells of the siRNA-SMAC group (P < 0.05) than in the siRNA-NC group. Compared with the pcDNA-NC group, the cell IC₅₀, cell clone number, cell invasion ability, and Bcl-2 protein and Bcl-2/Bax ratio were significantly lower in the pcDNA-SMAC group, the cell resistance index reversal was 2.51-fold, and the apoptosis ability and caspase-3, as well as Bax protein expression, were significantly higher (P < 0.05). Compared with the siRNA-NC group, cell IC₅₀, cell clone number, cell invasion ability, and Bcl-2 protein and Bcl-2/Bax ratio were significantly higher in the siRNA-SMAC group, and apoptosis ability and caspase-3 and Bax protein expression were significantly lower (P < 0.05). Conclusion High expression of SMAC increases paclitaxel sensitivity, inhibits cell growth and invasion, promotes apoptosis in lung adenocarcinoma cells, and has a regulatory effect on the caspase-3/Bcl-2/Bax signaling pathway.