Method for removing carbon tetrafluoride foreign matter in nitrogen trifluoride gas

The invention relates to a method to remove the carbon tetrafluoride in trifluorinated carbon. The invention uses azeotropic rectify to purify the NF3. it inlets the original gas and the entrainer into the rectify tower and go on the gas-liquid contacting continuously, the impurity forms the azeotropic thing with the much different gas steam point which is evaporated from the tower top and go into the second rectify tower to receive the entrainer; the entrainer and the NF3 are collected from the tower bottom and go into the third rectify tower; by using the boil difference if the NF3 and the entrainer, the high purify NF3 is get from the tower top, the entrainer is received from the tower bottom. The invention callbacks the entrainer by setting two towers and save the entrainer. The invention has decreased the CF4 content to 20ppm and decreased the condenser using mass. Also the device is simple and it costs low, has high efficiency.