Abstract: Drilling into formations containing flow water is always accompanied with severe mud losses, and conventional mud loss control methods are seldom succeeded in controlling this kind of mud losses. To control this kind of mud losses, a bentonite cement slurry lost circulation material (LCM) was developed. By increasing the content of the bentonite in the mixture slurry, the viscosity of the slurry can be increased, thereby improving the ability of the LCM to resist thinning by the flowing water. Research on the rheology, compressive strength and flow property of the bentonite cement slurry has shown that the optimum bentonite concentration in the mixture is 2% – 2.5% provided that the compressive strength of the slurry has met the operational requirements. The mobility of the bentonite cement slurry is apparently reduced after standing for 10 min before initial gelling, at this time it is in high viscosity state. Based on the property of the bentonite cement slurry, a pulse squeeze method is designed for field operation. By adjusting the flow rate of squeezing the slurry and the time interval between two squeezes, the high viscosity bentonite cement slurry is squeezed into the loss channels. If the slurry at its initial gelling time is pushed into the loss channels, it will stay there and become cementing, in this way a high success rate of operation can be achieved. Application of this technique in a field operation in Huabei Oilfield has shown that the bentonite cement slurry, combined with the pulse squeeze technique, is able to control severe mud losses into formations with flowing water successfully at the first try. This low-cost technique is easy to operate and has high success rate in field application.