Abstract: In view of rheology control problem for gas-to-liquid (GTL) based drilling fluid system, the influence of various factors on the rheological properties was studied. The results showed that the amount of emulsifier employed should be moderate, i.e., insufficient or excessive quantity will have a certain impact on the rheological properties. Further, organic clay, viscosifier, oil/water ratio and temperature are the main factors affecting the synthetic drilling fluid rheology. The organic clay content of 3%~4% is appropriate to a non-weighting drilling fluid, while 1.5%~3% content is desirable to a weighting drilling fluid. Usually the greater the density is, the smaller the amount of the organic clay is. The plastic viscosity and yield stress of a drilling fluid can be significantly increased with an increase of water content. Viscosifier and temperature have great influences on the viscosity and gels. Viscosifier dosage should be less than 1%, and a proper temperature resistant agent should be added at high temperatures.