A method for removing vapor within a heat pipe includes providing a predetermined amount of working fluid injected into the heat pipe. An opening is reserved at one end of the heat pipe. The opening is communicated with a vacuum environment. The communication between the opening and the vacuum environment is normally disconnected, such that at the instant the communication is connected ,the vacuum level of the vacuum environment is maintained at a certain range. The communication between the opening of the heat pipe and the vacuum environment is intermittently connected for several times. Within the duration while the communication between the opening and the vacuum environment is connected, the working fluid is evaporated without being boiled and vapor is exhausted from the opening.