Abstract: Components of natural gas have significant influence on its phase behavior during pipeline transmission, while thorough investigation on its phase behavior will help to avoid condensation and related hazards. Based on the gas-liquid equilibrium theory and combined with PR state equation and Van der Waals mixing rules, the influence of C₄-C₇ components on the phase behavior is analyzed by means of gas-liquid flashing calculation. Results show that the heavier components like butane, pentane, hexane, etc. can significantly influence the phase behavior of natural gas, while the light components has less influence on it. With the increase of the heavier components, the phase behavior curve has an obvious shift. The tiny raise of heavier components will obviously enhance the critical condensation pressure and temperature of pipelined gas and influence the phase behavior of gas. Among heavier components, the influence level of C₇ and C₈ is higher than C₆, and C₈ is higher than C₇ and C₆, remarkably. In project design, It will be incomplete if C₆₊ total content is used to analyze the phase behavior of natural gas, and it is necessary to study the characterigation of heavier components for natural gas and split method.