Abstract: Liquid scintillation (LS) counting has advantages in noself-absorption, simple sample preparation, and relatively easy application tomany radionuclides, especially for ³H which emits low energy β rays. The aim of this work is to calibrate the specific activity of the standard reference material of tritiated water to be developed, and the CIEMAT/NIST and TDCR methods were studied. The CIEMAT/NIST method with ⁵⁴Mn efficiency tracing was applied to standardize tritiated water on a Packard Tri-carb 3100TR spectrometer, and the combined standard uncertainty was 0.80%. The triple to double coincidence ratio (TDCR) efficiency calculation method requires a special LS-counter equipped with 3 photomultiplier tubes (PMTs) in coincidence, and could determine the specific activity through the information of coincidence counts. The tritiated water was also absolutely measured by the TDCR method, and the combined standard uncertainty is 0.66%. The results determined by the two methods are consistent with each other within E_n criterion.