Relative characteristics of XC and clay are discussed firstly, and the effects of the presence of clay, XC and the polyethylene glycol, and content of XC on drilling fluids are analyzed. The results show the interactions among NaCl, KCl, clay, polyethylene glycol and XC greatly affect the rheological behavior of drilling fluids, and there is a critical temperature in the low-temperature range at which the viscosity of drilling fluids increases rapidly. Adding clay increases viscosity and fluid loss of drilling fluids. With temperature higher than critical temperature, increment of the content of KCl and XC may reduce viscosity, and also reduces the low-temperature fluid loss later. With temperature lower than critical temperature, content of KCl should be reduced in order to avoid rapid increment of viscosity. For relative drilling fluid system, 5% polyethylene glycol with a molecular weight of 10000 and 0.25% XC combined with 15% NaCl + 5% KCl or 20% NaCl are suitable.