Abstract: Tumor tissues are often composed of not only tumor cells but also non-tumor cells such as immune cells, stromal cells and mesenchymal cells. They play an important role in tumor growth and progress together. Tumor purity is significantly associated with clinical features, gene expression and tumor biology, indicating that we need to fully consider the potential confounding effect of tumor purity on tumor analyses. This article reviews the concept, calculate methods and impact of tumor purity on genomic analysis.