Abstract: According to the problem of unconsidering the influence of gas component on testing gas pressure with the indirect method. Using Dalton partial pressure law, the gas pressure calculation of different gas component is modified. The results show that the gas pressure can be calculated directly by the Langmuir equation When the CH₄ component of the gas mixture is greater than 90%, and the error is less than 5%, when CH₄ component of gas mixture is less than 90%, the partial pressure must be calculated firstly by using the law of partial pressure, then the pressure of the mixed gas is calculated. The error of gas pressure is within 5% after correction. The accuracy could meet the needs of engineering.