Abstract: Considering and to avoid the effect of competitive adsorption on the stationary phase of co-existing components with the solute (i.e.the component to be determined) in the gas-phase on the accuracy of results qualitative and quantitative analysis of the solute by gas chromatography,an equation describing the relationship between the amount of sample injected and the retention factor of the solute molecules was proposed.Two important parameters which were characteristic in gas chromatography,were obtained by this equation,i.e.the thermodynamic equilibrium constant (Ka),of competitive adsorption of the solute and other co-existing components,and amount of the solute (NmS) capable to be adsorbed on unit volume of the stationary phase.When other operation parameters of the chromatographic system were fixed,the relationship between the amount of solute in sample injected and the retention factor was directly characterized by the magnitude of the value Ka.The proposed equation was tested by experiments with toluene in 3 different gas chromatographic systems,and its feasibility was proved priliminarily.