Objective  To investigate the effect of microRNA(miR)-140-3p targeting cell division cycle associated 8(CDCA8) on invasion and metastasis of lung adenocarcinoma cells.    Methods  The differentially expressed miRNAs were analyzed by GEO2R in GEO database. The target genes of miR-140-3p were searched by TargetScan human7.2 and miRWalk databases. The hub gene was screened by Cytoscape 3.7.2 software. GEPIA database was used to query the expression levels of target gene in lung adenocarcinoma tissues and normal lung tissues, the expression levels in different stages of lung adenocarcinoma, and the relationship between the expression levels of target gene and the overall survival rate of lung adenocarcinoma patients. The survival analysis of mi-140-3p in lung adenocarcinoma and the correlation between miR-140-3p and CDCA8 expression levels were searched in starBase database. Real-time PCR was used to detect the expression levels of miR-140-3p in normal lung epithelial cells BEAS-2B and lung adenocarcinoma cells A549, as well as the efficiency of infection. Expression levels of CDCA8 mRNA and protein were detected by Real-time PCR and Western blotting experiments after overexpresion of miR-140-3p. Dual-luciferase reporter assay verified whether miR-140-3p directly binds to CDCA8. Transwell invasion assay detected the effect of overexpression of miR-140-3p and CDCA8 on the invasiveness of lung adenocarcinoma cells.    Results  Analysis result  from GEO and other databases showed that the expression level of miR-140-3p in normal lung tissues was significantly higher than that in lung adenocarcinoma, and its predicted target gene CDCA8 expression level in lung adenocarcinoma was significantly higher than that in normal lung tissues, and CDCA8 was negatively correlated with the expression level of miR-140-3p in lung adenocarcinoma. The experimental result  showed that the expression of miR-140-3p in A549 cells was significantly lower than that in BEAS-2B cells (P＜0.05). The expression level of miR-140-3p increased significantly after lentiviral infection (P＜0.05). CDCA8 mRNA and protein expression levels were significantly down-regulated after overexpression of miR-140-3p (P＜0.05). Dual-luciferase reporter assay result  showed that miR-140-3p could directly bind to CDCA8 (P＜0.05). Compared with the control group, overexpression of miR-140-3p inhibited the invasion and metastasis of lung adenocarcinoma A549, while CDCA8 revrsed the inhibition of miR-140-3p on the invasion and metastasis of lung adenocarcinoma A549 (P＜0.05).    Conclusion  MiR-140-3p targeting CDCA8 inhibits the invasion and metastasis of lung adenocarcinoma cells.