Abstract: In order to enhance the comprehensive performance of dry gas seal of supercritical carbon dioxide near the critical point, a combined spiral groove consisting of a wide spiral groove and a narrow spiral groove was designed based on the superposition combination principle. Considering the actual gas effect, inertia effect and turbulence effect, the geometric parameters of the combined spiral groove were changed to establish the corresponding mathematical model, so as to calculate the pressure distribution of gas film at the end face. Results show that under the influence of centrifugal effect, inertia effect and viscous pumping, the sealing performance of the combined spiral groove improves with the increase of the groove length and number of grooves, and reduces with the increase of groove depth, spiral angle and gas film thickness. At the groove length of 69 mm, the slot depth of 5 μm, the number of grooves of 12, the helix angle of 15° and the gas film thickness of 2.05 μm, stiffness to leakage ratio of the dry gas seal reaches the maximum, and the comprehensive sealing performance is the best.