The effects of the operation conditions, such as reaction time, introduction of preheating stage, temperature of starting stir, preheating stage time, and final stir speed, on the physical properties of the polyethylene wax producted in a loop reactor by thermal degradation were investigated. As the reaction time increased, the viscosity and the softening point of the products were decreased. The viscosity, Mn and Mw of the final products were increased with an increase of the temperature of starting stir due to a decrease of heat transfer rate. When the preheating stage time was 60 min, the viscosity, Mn and Mw of the final products showed the minimum values, respectively. As the final stir speed increased, the viscosity, Mn, Mw and Mw/Mn of the final products were decreased due to an increase of heat transfer rate. The deepness of the top void showed the minimum value when the medium temperature reached at about 380 ℃ because thermal degradation of the medium took place in good earnest at the temperature. The effects of the operation conditions on the softening point of the final products and the yield were negligible.