A method for preparing high-purity tellurium based on viscous distillation and gas-phase separation was developed. By adjusting the condenser structure and condensing temperature to achieve viscous distillation, the dominant condensation zone for tellurium was controlled; hence, poorly volatile substances remained in the crucible, while selenium was separated from tellurium in the gas phase to achieve the purification of metallurgical-grade crude tellurium. Specifically, the saturated vapor pressure, mean free path of tellurium, impurity distribution, and morphologies of the condensate at different locations were investigated in detail. The results for a 500 g upscaled experiment showed that the direct yield of Te was 83.40%, the purity of Te reached higher than 99.9996 wt.% and the selenium content in the dominant condensation zone was reduced to 2.76×10^-4 wt.% under the optimal experimental conditions of 5 Pa, 773 K and 90 min.