Studies have confirmed that human cytomegalovirus (HCMV) infection may be associated with certain malignant tumors. Oncomodulation suggests that HCMV can infect tumor cells and influence their malignancy and in this particular case increase it. Some clinical studies show that the number of HCMV infected tumor cells has been implicated in the degree of tumor malignancy in patients with glioblastoma, suggesting that HCMV may exert oncostimulatory effects. Influencing the cell cycle, blocking apoptosis of the infected cells, influencing the malignant behavior of tumor cells, and so on, may contribute to the oncomodulatory effects of HCMV. An investigation into the molecular mechanisms of such oncomodulatory effects of HCMV will be significant to expand the prevention and treatment of cancer.