Abstract: Natural gas compressibility factor Z is one of the most important physical parameters in the natural gas engineering calculations, and the determining methods mainly include Standing-Katz chart method, laboratory experiments method, equations of state law method and the empirical formulas method. Due to the usage limitations of the former two methods, the application advantages of equations of state law method and the empirical formulas method become increasingly evident. In this paper, the calculation accuracy of equations that calculate compressibility factor based gas composition was evaluated. The equations include AGA8-92DC, Piper-DAK, Piper-Mahmoud, Elsharkawy-DAK and Elsharkawy-Mahmoud. These five calculation formulas to be valuated were written into Visual Basic 6.0 and 113 measured values of acidic lean gas compressibility factor were used to compare with the calculated values of these five formulas. The comparison indicates that firstly for the lean gas with carbon dioxide at low pressure or medium pressure, the calculation error of AGA8-92DC is less than others; secondly, for the lean gas with hydrogen sulfide and carbon dioxide at low or medium pressure, the calculation error of Piper-Mahmoud is minimal compared to the other correlations. In addition, this study presents that when the temperature of natural gas increases, the errors of calculated values by these five formulas will all decrease compared with the original calculation errors.