Heat pipe used to cool chips and heat source is widely applied to the
electronic equipments, such as notebooks, 1U Servers and other heat-removed systems. Theoretically, it can be designed from input parameters, related to thermodynamic properties of the working fluid and the geometry factors of the heat pipe. However, only few researches mention about the accuracy of the theoretical model for Qmax due to the reason that the Qmax is not easy to obtain from experiments.This paper not only presents a theoretical model that predicts the maximum heat transfer rate (Qmax) for a round shape heat pipe, but also obtains Qmax values with different lengths of the evaporator and the condenser. The effect of the different operating temperature and the different diameter of the heat pipe on the Qmax were also shown in this study.All these data will be a very good benchmark for the comparison of the experiment and the simulated results. From the experiment, the Qmax was rising with the increasing amount of the heat pipe diameter and the operating temperature. The deviation value of the Qmax between simulations and experiments are less than 15 %. It means that the Qmax model is a very good tool for designing the heat pipe performance ability.