Lung adenocarcinoma (LUAD) is usually diagnosed at advanced stages. Hence, there is an urgent need to seek an effective biomarker to predict LUAD status. Long noncoding RNAs (lncRNAs) play key roles in the development of tumors. However, the relationship between LINC00921and LUAD remains unclear. The gene expression data of LUAD were downloaded from the Cancer Genome Atlas database to investigate the expression level of LINC00921in LUAD. Diagnostic ability analysis, survival analysis, tumor mutational burden analysis, and immune cell infiltration analysis of LINC00921in LUAD patients were performed simultaneously. According to the median expression value of LINC00921, patients were divided into LINC00921high- and low-expression groups. The function of LINC00921in LUAD was identified through difference analysis and enrichment analysis. Moreover, drugs that may be relevant to LUAD treatment were screened. Finally, blood samples were collected for real-time polymerase chain reaction. LINC00921was significantly lower in LUAD tumor tissues. Notably, patients with low expression of LINC00921had a shorter median survival time. Decreased immune cell infiltration in the tumor microenvironment in the low LINC00921expression group may contribute to poorer patient outcomes. Tumor mutational burden was significantly different in survival between the LINC00921high- and low-expression groups. In addition, LINC00921may exert an influence on cancer development through its regulation of target genes transcription. Glyceraldehyde-3-phosphate dehydrogenase-related drugs may be more likely to be therapeutically effective in LUAD. LINC00921was able to be used as the potential diagnostic indicator for LUAD.