Abstract: In order to satisfy the safety drilling requirements in "narrow density window" formation,"liquid volume stable" managed pressure drilling was investigated.Based on the analysis of wellbore pressure,problems and deficiencies of managed pressure drilling were determined,and "liquid volume stable" managed pressure drilling method was proposed.Based on the balance between formation pressure and downhole pressure,the method involves keeping stable circulation fluid volume during drilling,and pipe connection under shut-in,shut-in during trip and keeping fluid in wellbore stable by squeezing in and releasing liquid,so as to keep pressure in wellbore balanced.By controlling the "liquid volume stable" to achieve balance between bottomhole pressure and formation pressure,is an effective way to achieve balanced pressure drilling.The technique had been successfully used in high pressure,ultra saturated,narrow density window brine formation drilling,forming a special drilling technology.Key points and related calculation method had been put forward,providing a new approach for research and application of managed pressure drilling.