Abstract: The substance's thermodynamic functions (heat capacity, entropy, enthalpy) were commonly used in the rocket engine's thermal property analysis. According to the thermodynamic relation, the three functions above can be expressed as polynomial on temperature with the same seven factors. Due to the technological progress, newer and more precious data at different temperatures were demanded. The function data were divided into different intervals based on temperatures, to ensure the calculated data were equal at adjacent intervals, with the least square method and program calculating, 135 kinds of substances' temperature coefficients were redefined. And the above substances' calculated thermodynamic functions from 300 K to 5 000 K were determined. Furthermore, to get more precise values, the heat capacities of 26 substances such as nitrogen atom, liquid lead, crystalline silicon, which had larger relative errors were corrected by using the least square method and the precision of heat capacities is 100 times higher than before. Compared with the standard data, the calculated data have small error and high precision and can be applied to many disciplines.