An experimantal study on how the length of sintering effect the heat transfer performance of composite-wicked heat pipes is presented in this study. The sintering length is 1/3,2/3 or 1 of the total length of the heat pipe(named GO, GT and GF) with outer diameter of 8mm which is made by using mandrel with diameter of 5.5mm and 6mm.Working fluid is filled in two methods:(1)filling all pore of wicks(2)filling the same quility. There are several conclusions according to the investigation of maximum heat transfer power(MHTP), evaporator thermal resistance, condenser thermal resistance and the total thermal resistance(Rtotal): The method of filling working fluid has less effect on the thermal resistance but more on the MHTP. With mandrel in diameter of 5.5mm, the MHTP of GO,GT and GF all get more than 100W in method (1), while GF only get 80W in method (2). With mandrel in diameter of 6mm, the MHTP of GO,GT and GF get more than 100W,80W and 60W respectively in method (1), while get 80W, more than 100W and 80W respectively in method (2). Reducing the length of sintering results in the Rtotal of heat pipe decreasing. The Rtotal of GO and GT can reduce 33% relative to GF with the same wick thickness. The Rtotal of the heat pipe change less than 0.01℃/W with input powder varies from 60W to 100W. When the wick thickness 0.25mm thicker, the difference of Rtotal of heat pipes with the same sintering length is also less than 0.01℃/W. Both methods showed that the length of sintering has less effect on the evaporator thermal resistance but have more effect on the condenser and the total thermal resistance, in which the condenser thermal resistance is of the same trend with the total thermal resistance.