A Closed Loop Pulsating Heat Pipe (CLPHP) is a complex heat transfer device with a strong thermo-hydrodynamic coupling governing its thermal performance. This research utilized 6 mm outer diameter and 3 mm inner diameter glass tubes to manufacture 9 turns closed loop Pulsating Heat Pipe(PHP) with a total length of 1980mm. For achieving the loop circulation easily, a water cooling system kept at 25 ℃ was used as the condenser, and used methanol as working fluid. Experiment was conducted to measure temperature difference and to evaluate the thermal resistance under at a series change of power inputs (30W, 60W, 90W, 120W, 150W, 180W). A digital video camera was used to record the working situation of the working fluid inside the channel. The flow pattern can be categorized into clockwise, counter-clockwise and transition status. The results showed the flow direction of PHP was changed with the temperature difference of tubes. The lowest resistance is 0.217(K/W) at an input power of 180W in this study.