the aligned carbon nanotube arrays are mixed with distilled water by firstly vacuuming the aligned carbon nanotube arrays to remove air therein and then filling the distilled water in the aligned carbon nanotube arrays the aligned carbon nanotube arrays filled with distilled water are then cooled to form a composite material of carbon nanotube arrays combined with water finally incises the carbon nanotube arrays from the substrate in a manner that the carbon nanotube arrays have a predetermined length thus the carbon nanotube arrays 15 are obtained when assembled the bottom surface 122 of the bottom wall 12 is thermally attached to the heat generating component 20 and a top surface 146 of the top wall 144 is thermally attached to the chassis 31 of the heat sink 30 as the heat generated by the heat generating component 20 which is attached to the bottom surface 122 of the bottom wall 12 is transferred to the heat spreader 10 the working fluid contained therein absorbs the heat and evaporates into vapor since the vapor spreads quickly it quickly fills an interior of the heat spreader 10 and whenever the vapor comes into contact with cooler wall of the heat spreader 10 i e the top wall 14 of the heat spreader 10 which thermally contact with the heat sink 30.