The system of measurement while drilling(MWD is usually used in the condition of high temperature,high pressure and strong vibration,while the traditional sealing structure of Orings may cause leakage easily in those working condition.According to the sealing demand of the sealing structure of small MWD used at the well bottom of 3 000 m,a new conical sealing structure based on the Orings was designed.The sealing structure adopts the end face seal as the first seal,the Orings and the conical sealing as the second seal and the thread sealed as the third seal.The designed sealing structure was tested many times at drilling field.The result indicates that the sealing structure can work safety more than 20 hours and it can meet the requires of real project.