The heat capacity Ｃpof ThO2 can be calculated as the phonon part of Ｃp for other actinide dioxides used as fuel in nuclear reactors. Precise determination of the phonon part of Ｃp of actinide dioxides is helpful to find out the contributions of other factores to Ｃp. In this paper we have, through studying the heat capacity of ThO2, developed a general method applicable to the study of Ｃp of other solids. In the developed method the three type-different experimental measurements made on a solid-heat capacity, thermal expansion and Debye-Waller factor-can be brought together for comparison. The application of this method to the study of Ｃp of ThO2 has enabled us to propose a better description of Ｃp of ThO2 than the generally accepted expression.