Abstract: The advantages of the direct measurement method for absorbed dose to water in Report TRS-398 were studied. This is a promising method for determining prescription dose in clinical applications and reducing the uncertainty of clinical radiotherapy dosimetry. By introducing the conditions and methods for directly measuring the absorbed dose to water under different kinds of radiation, part of the experimental data based on TRS-398 report measurement method is summarized. The results show that the repeatability of the direct measurement method is less than 0.5% and the uncertainty of dose measurement is less than 2%. The direct measurement method for absorbed dose to water meets the uncertainty requirement of clinical dose outputs, i.e. less than 5% (k=1). These results provide a theoretical basis for updating the method of dose output measurement in clinical radiotherapy.