Abstract: The density change of heavy oil after injecting gas influences the lifting efficiency directly. In order to improve the production efficiency of Tahe heavy oil, the study of mixed density of natural gas injected into super heavy oil in Tahe oilfield was carried out. The results showed that the mixing density decreases quasi-linearly with the increase of temperature and oil-gas ratio. Based on the experimental data, the Obomanu model of calculating heavy oil-gas mixture density is modified, and the density model of Tahe crude oil with gas injection is established. The correlation coefficient R² of Obomanu model is 0.670 3-0.769 2, the correlation coefficient R² of modified model is 0.985 2-0.998 9, the fitness degree of modified model is enhanced by 30%, which is suitable for low and high pressure conditions. The balance pressure-density-gas oil ratio map of oil-gas mixture is established, and it can guide the gas production with heavy oil injection.