The present invention relates to a method for sealing a heat transfer unit, which includes the steps of providing a heat transfer unit having at least one opening, welding the opening to form a welding section and close the opening, and pinching off the welding section and cutting part of the welding section to form a cutting end and complete sealing the opening of the heat transfer unit. By means of the method of the present invention, an extremely short dead zone can be obtained and high heat conduction efficiency is enhanced, further having the effects of reducing the arrangement space and shrinking steps of the heat pipe.