ing at the influence of the focus point position of optical path in the infrared solar occultation flux method alignment system on the spectral quality and inversion accuracy of the gas mass concentration, the reference coordinates are established, the geometric optical path in the interference cavity is derived, and a new infrared spectral correction algorithm is proposed in this paper. Using ZEMAX software to simulate and analyze the off-axis condition of the optical path in the interference cavity, and the results show that the change of focus point position will cause the size, position and intensity of the light spot on the mercury cadmium telluride detector. The results of field experiments show that the change of off-axis angle of the beam will cause the change of interference intensity and signal-to-noise ratio of the beam. In the case of static measurement, the average drift of SF₆ wavenumber of the traditional algorithm and the algorithm are 0.2602 cm ^-1 and 0.1146 cm ^-1, respectively. In the case of dynamic measurement, the average drift of SF₆ wavenumber of the traditional algorithm and the algorithm are 0.2355 cm ^-1 and 0.0860 cm ^-1, respectively, and the accuracy of inversion of gas mass concentration is higher by using the algorithm.