Based on the study of leakage characteristics of labyrinth seal structure (LSS), a new type of combined seal structure (CSS) consisting of the labyrinth structure and the nozzle structure has been proposed. The sealing characteristics of CSS and LSS are compared by means of numerical simulation and experiments, and the effects of the internal resistance of the device, structural geometric parameters and other factors on the leakage characteristics of CSS are studied. The results illustrate the following conclusions: (a) When the inlet flow is 12 m3/h and the internal resistance of the device is 2,000-4,000 Pa, the leakage rate of CSS decreases by 30%-40% in comparison with that of LSS, which indicates that the performance of CSS is much better than that of LSS. (b) The leakage rate increases as the internal resistance of the device increases. When the internal resistance of the device increases from 2,000 Pa to 8,000 Pa, the leakage rate increases from 26% to 72%. (c) When the internal resistance of the device is constant, the larger the inlet flow, the smaller the leakage rate. d) The choice of nozzle radius in structural geometric parameters is more important for the leakage rate than the tooth height and teeth numbers. When the nozzle radius decreases, ?PAB (pressure difference between the labyrinth structure and the nozzle structure) and the leakage rate decrease accordingly.