Objective To investigate the relationship between the expression of mast cell expressed membrane protein 1 (MCEMP1) in gastric cancer and its relationship with prognosis and tumor immune infiltration. Methods Transcriptome expression profile data and clinical data information of gastric cancer and normal samples were downloaded from TCGA database, and differentially expressed genes in gastric cancer tumor microenvironment were extracted using R 4.0.5 software. Protein-protein interaction network of differentially expressed genes was constructed by using STRING online website, protein-protein interaction network and univariate Cox proportional hazards regression analysis were used for cross-tabulation analysis to obtain key genes. Kruskal-Wallis rank sum test was used to investigate the correlation between key genes and clinicopathological features. The possible signaling pathways involved in key genes were predicted by gene set enrichment analysis. We further analyzed the relationship between expression of key gene and the level of immune infiltration and immune molecules in gastric cancer by TISIDB online database and CIBERSORT algorithm. Results A total of 760 differentially expressed genes in gastric cancer were found and a key gene of MCEMP1 was derived from cross-tabulation analysis based on the results of protein-protein interaction network and univariate Cox proportional hazards regression analysis. Expression of MCEMP1 was significantly upregulated in gastric cancer tissues (P<0.001), and survival analysis showed that the overall survival rate of the group with high expression level of MCEMP1 was lower than that of low expression [HR=1.176, 95%CI (1.066, 1.297）, P=0.046]. Expression of MCEMP1 also correlated with age, T-stage, and clinical stage of gastric cancer (P<0.05) , and expression of MCEMP1 was significantly associated with a variety kinds of immune cells and expression of immune molecules (P<0.05). Conclusion MCEMP1 is a potential prognostic marker for gastric cancer and is associated with immune infiltration in gastric cancer.