Abstract: A thermal vacuum analytical system is established for determination of tritium in environmental soil samples. The effects on tritium recovery of the efficiency of catalyst oxidation, condenser recovery and analytical coefficient have been studied. Results prove that efficiency of catalyst oxidation is 98.6 %, efficiency of recovery of condenser is 99 %, analytical coefficient is 97.8 % when soil samples have been heated for 3 h at 550 ℃. This system can meet the need of determination of tritium in environmental soil samples.