Abstract: Quenching effect is always existed in the radioactivity measurements using liquid scintillation counting method and the quenching level is different for almost every samples, which influences the measurement accuracy and precision. Therefore quenching correction should be made in tritium radioactivity measurements for water samples when liquid scintillation method is used. In this paper, the tritium external standard calibration method was used for the correction of quenching effect. Through the experiments, the quenching calibration curve, namely the relationship between counting efficiency (E) and scintillation quenching parameter SQP, E=0.0013SQP(E)-0.7076, was established. The calibration method has been applied to the liquid scintillation measurements of tritium radioactivity in water samples with satisfactory results.