The application of Co (Ⅲ)/Al2O3 catalyst in Fischer-Tropsch synthesis (FTS) was studied in a wide range of synthesis gas conversions and compared with Fuzzy Simulation results.Present study applies fuzzy model to predicting the product composition of CH4,CO2 and CO in Fischer-Tropsch process for natural gas synthesis,in which the input vector was 4-dimension including four variables (operating pressure,operating temperature,time and CO/H2 ratio) of 70 different experim.ents and the output product is a composition of CO2,CO and CH4.The Mamdani algorithm has been applied to the training of the fuzzy system and the test set was used to evaluate the performance of the system including R2,ARE,AARE and SD.The results demonstrated that the predicted values from the model were in good consistency with the experimental data.The work indicates how fuzzy inference system (FIS),as a promising predicting technique,would be effectively used in FTS.