In order to improve the tracing accuracy of infrared seeker and to reduce the influence imposed by the gas tube disturbances, a variable gain disturbance observer (VGDOB) is put up forward. First, based on the control system design platform of infrared seeker, disturbance characteristics is analyzed. Second, according to the characteristics of the gas tube disturbances and traditional disturbance observer theory, VGDOB is designed and its robust stabilization is also researched. Finally, experiment is implemented to restrain the gas tube disturbances by using the VGDOB. Experimental results indicate that with VGDOB, the velocity step response accuracy of the system is improved by 71.1%, and the position step response accuracy of the system is increased by 42.8%, while the traditional disturbance observer cannot compensate the gas tube disturbances. It can be concluded that the VGDOB can suppress the gas tube disturbances that exist in the infrared seeker effectively.