A heat pipe comprises a flat tube and a wick structure. The flat tube includes a hollow chamber and has a front and a rear sealed ends along an axial direction. The wick structure is disposed in the hollow chamber and extended along the axial direction of the flat tube. The wick structure is divided into a front, a middle and a rear sections sequentially along the axial direction. The front section is near the front sealed end, the rear section is near the rear sealed end. The front, middle and rear sections have a maximum length parallel to the width direction, respectively, the maximum length of the middle section is greater than that of the front section and that of the rear section so as to be used as the evaporator of the heat pipe.