Abstract: During the pipeline transportation of oil and gas, hydrate tends to form in the working condition of lowtemperature and high pressure and consequently influences the pipeline transportation efficiency and even leads to pipelineblockage. In practical engineering, the formation of hydrate is usually prevented by adding thermodynamic inhibitors.And the commonly used thermodynamic inhibitors include methanol (MeOH), ethylene glycol (EG), and so on. Therefore, the determination of the reasonable dosage of thermodynamic inhibitor is of great significance to the safety and economyof pipeline operation. In this paper, a method for calculating the formation equilibrium condition of hydrate containinginhibitor system was established on the basis of Chen-Guo dual-process hydrate thermodynamic model, after the activity ofwater in water-alcohol solution was determined in Wilson Model. Then, the idea of estimation-trial-adjustment was proposedto determine the critical minimum dosage of inhibitor in the working condition of pipeline operation. It is verified that themethod is simple and accurate, and can meet the needs of practical engineering.