Abstract: During Managed Pressure Drilling（MPD）, BHP（Bottom Hole Pressure）can be controlled through adjusting surface back pressure, so drilling operation is always under control. With this advantage, MPD can solve the complicated geologic problems and avoid loss kick scenario by using surface back pressure, and it is a good solution for drilling narrow operational window formation.. MPD can be divided into 4 types of sub-drilling method, but this paper will focus on one which is Constant Bottom Hole Pressure Drilling（CBHP）. This paper provides the definition of MPD and analyzes the theory, benefits and equipment needed for CBHP operation and also the field application on the Frass-0001 Well in Saudi Arabia.