Calculation of isochoric molar heat capacity refers to extensive utilization of chemical thermodynamics, numeric analysis, computer programming and so on, which is favorable for cultivation of students’ comprehensive application. Various researches have revealed significant effect of volume (or pressure) on isochoric molar heat capacity of non-ideal gases. On basis of non-ideal gaseous state equations, the isochoric molar heat capacity CV at (p2, T) is calculated under the condition of experimentally or literarily known CV at (p1, T). Comparison between calculation values and literature ones is carried out. The results show that CV is affected considerably by pressure at low temperatures (<400K) and high pressures (>10MPa); effect of elevated pressure can not be ignored, whereas CV is affected slightly at high temperatures or low pressures