A large number of published papers reveal that gas-to-liquid (GTL) fuel has the potential for reducing the particulate matter (PM), CO, and hydrocarbon (HQ emissions to a certain degree, and NOx emissions can also be reduced by optimizing the engine parameters or at a larger exhaust gas recirculation (EGR) rate. To reduce the PM and NOx emissions simultaneously on a larger scale, an experiment was conducted of GTL combustion and emissions on a single-cylinder diesel engine with the port fuel injection (PFI) of methanol. The results revealed that, because of the lower cetane number and larger latent evaporation heat value of methanol, the ignition timing delayed clearly, the maximum in-cylinder gas pressure decreased, and the maximum heat release rate increased with the PFI of methanol. At a lower to medium overall equivalence ratio, the maximum in-cylinder gas temperature decreased linearly with the increase of the premixed ratio of methanol. At a large overall equivalence ratio, the maximum gas temperature decreased on a small scale at first and then began to increase in a small magnitude with the increase of the methanol addition. With regard to the regulated emissions, both CO and HC emissions increased with the addition of methanol. However, it was interesting to note that a tradeoff relationship of PM and NOx was changed by PFI of methanol, the NOx emissions could be reduced by 85-98%, and the smoke opacity decreased by 50-62% in overall operating ranges.