Objective To investigate the promoting effect of S-adenosyl-homocysteine hydrolase (AHCY) on the proliferation of lung cancer cells and its regulatory mechanism on the expression of methionine adenosyltransferase 1A (MAT1A). Methods Wayne plot analysis was performed on four lung cancer data chips, including GSE103512, GSE18842, GSE20189, and GSE102286, to screen for differentially expressed key genes. Protein immunoprecipitation assay was used to detect the interaction between AHCY and MAT1A. pAdTrack-CMV-NC+pCV702-NC (NC), pAdTrack-CMV, and pAdTrack-CMV+pCV702 were transfected into A549 and PC9 cells, respectively. The cell proliferation, apoptosis, the mitochondrial membrane potential, the ROS levels in cells, the total RNA methylation levels in cells, and the expression of AHCY and MAT1A in cells were detected, sequentially. Results The statistical analysis identified AHCY and MAT1A were the key differentially expressed genes across the four datasets. Co-immunoprecipitation experiments confirmed a direct interaction between AHCY and MAT1A in lung cancer (P<0.05). Upregulation of the expression of AHCY could significantly increase the proliferation of A549 and PC9 cells, decrease the cell apoptosis, increase the mitochondrial membrane potential, alleviate the intracellular reactive oxygen species levels, and decrease the total RNA methylation levels, while MAT1A overexpression partially reversed the promoting effects of AHCY on lung cancer cells. All differences were statistically significant (all P<0.05). Conclusions The expression of AHCY is significantly increased in lung cancer, while the expression of MAT1A is significantly decreased in lung cancer. High expression of AHCY can promote the cancer cell proliferation and affect total RNA methylation, while downregulate the expression of MAT1A in lung cancer cells.