According to physical properties of the tar and separate requirements, a type of tar separator which is applicable to dry method of removing the tar was designed. This type of tar separator can cool and condensing the tar, at the same time separates the droplets of the tar. It can be seen from the numerical simulation results of gas flow field, the results of gas movement of heat transfer show that wall cooling has a great influence on temperature field in the cyclone separator. The temperature field also presents the characteristics that the surrounding area gradually reducing with surrounding downward flow, and the central zone rising up with centering upward flow, and the radial temperature gradually reducing in the cyclone separator. The decrease of temperature leads to the increase in gas density and the decrease in gas viscosity and the increase in the tar droplets viscosity. Wall cooling can reduce the cut size, as well as improve the separation efficiency of biomass gasification gas tar through the tar droplet separation theory and the physical analysis of tar.