Growing studies have shown that non-SMC condensin I complex subunit G (NCAPG) was highly expressed in a variety of tumors and was involved in the progression of multitumors, but the role of NCAPG in tumorigenesis is not fully understood. Our study purposed to systematically investigate the role of NCAPG across cancer types. Interacting molecules with NCAPG were analyzed using searching bioinformatics websites including Search Tool for the Retrieval of Interacting Genes/Proteins, GeneMANIA, and Global Positioning System-Prot. NCAPG-related diseases were acquired using the Open Targets Platform. The interaction of NCAPG and 14 cancer functional states was achieved using the CancerSEA website. The databases including the University of California Santa Cruz Xena, Genotype-Tissue Expression, The Cancer Genome Atlas Program, Human Protein Atlas, and XIANTAO Academic were used to interpret the expression of NCAPG. Correlations between NCAPG expression and immune infiltration and immune-related molecules were analyzed by using Tumor Immune Estimation Resource Version 2 and Tumor and Immune System Interaction Database databases. NCAPG expression was significantly upregulated in most cancer types. NCAPG was identified as a marker of diagnostic value and prognostic significance in most cancer types. NCAPG expression was related to immune cell infiltration and immune-related molecules across various cancers, especially kidney renal clear cell carcinoma and thyroid carcinoma. Furthermore, NCAPG expression could affect the enrichment and decrease immune cell infiltration to influence prognosis in kidney renal clear cell carcinoma but was devoid of evidence in thyroid carcinoma. NCAPG was a prospective marker for the diagnosis and prognosis of pan-cancer. Our results suggested that NCAPG was a potential cancer biomarker for the diagnosis and prognosis of pan-cancer. NCAPG might affect the immune microenvironment, which could be applied in the development of new-targeted drugs for immunotherapy.