Abstract: Wellhead pressure in case of any emergency well shut-in is a very important parameter in wellhead equipment and pipeline selection,but theoretical calculation method of well head pressure is not available yet.Water hammer pressure is mainly affected by fluid rate,pressure wave propagation velocity and fluid density.The calculation method of wellhead pressure resulting from water hammer pressure and bottom pressure buildup is established.Considering the influence of water hammer pressure and shut-in pressure buildup,the change of wellhead pressure in case of emergency well shut-in is studied.The study shows that wellhead pressure in medium to high permeability reservoir would increase vs.time.The longer the well shut-in time,the higher the wellhead pressure would be.The wellhead pressure for production in low permeability reservior may increase in a sudden.