The invention relates to a method for precisely measuring the internal temperature of an alkali metal air chamber based on mixed optical pumping, and the method comprises the steps: heating the alkali metal air chamber filled with K and Rb atoms to a lower start temperature, measuring the laser absorption spectrum of K and Rb atoms, carrying out the fitting calculation through a theoretical formula, and obtaining the densities of K and Rb atoms under the start temperature, jointing the Raoult's law simultaneously, obtaining the start temperature and the saturated vapor pressure of K and Rb atoms under the start temperature, and calculating the mole fraction ratio of K and Rb atoms; heating the air chamber to to-be-measured temperature. Because the density of Rb atoms nearby a resonant point in an SERF state and the absorption is intense and there is a big deviation in the density of Rb atoms obtained through curve fitting, the method employs a spectrum absorption method to obtain the density of K atoms, and obtains the to-be-measured temperature through combination with the mole fraction of K atoms. The method can be used for the precise measurement of the internal temperature of the alkali metal air chamber employed by an atom magnetometer based on mixed optical pumping and an atom spinning gyro.