The ratio of alkali metal mixture is one of the most important parameters in gauge head belonging to the ultra-sensitivity inertial measurement equipment,which is required to detect precisely.According to the feature that ratio of alkali metal is related to alkali metal vapor density,the theory of optical depth is used to detect the ratio of alkali metal in the present article.The result shows that the data got by the theory of optical depth compared with empirical formula differs at three orders of magnitude,which can’t ensure the accuracy.By changing the data processing method,model between spectral absorption rate and temperature in cell is established.The temperature in alkali metal cell is calibrated by spectral absorption rate.The ratio of alkali metal atoms in the cell is analyzed by calculating the alkali density with empirical formula.The computational error is less than 10%.