Inhibin subunit beta A (INHBA) is a member of the TGF-beta (transforming growth factor-beta) superfamily proteins, which plays a fundamental role in various cancers. However, little is known about the exact role of INHBA in patients with gastric cancer (GC). The present study aims to explore the relationship between INHBA and GC and detect the underlying mechanisms. Multiple bioinformatic approaches were first preformed basing on TIMER, GEPIA2, GEO, Oncomine and UALCAN databases, which revealed that INHBA was highly elevated in GC. This result was proved by Immunohistochemistry (IHC) and real time polymerase chain reaction (RT-PCR) in 65 cases of GC tissues in our study. The bioinformatic analysis also revealed that high expression of INHBA was significantly related to unfavorable prognosis of GC. To detect the underlying mechanism, further analysis was performed basing on Kaplan Meier plotter database and found that poor prognosis of GC was related to infiltration of different enriched immune-cell subgroups. That was INHBA being negatively correlated with B cell while positively correlated with CD8 + T cells, macrophage, neutrophil and dendritic cell infiltration. However, there was week significant methylation level change between tumor and normal tissues. Moreover, INHBA mainly enriched on cancer-related signaling pathways, including TGF-beta signaling pathway, ECM-receptor signaling pathway, PID ALK1/2 pathway, and AGE-RAGE signaling pathway, which provide a new insight for future in-depth study.