This paper presents the results of theoretical study on finding the design parameters of solar gravity heat pipe used to supply hot water in Ho Chi Minh city. The results show that, the solar gravity heat pipe should be installed with the inclined angle about 20°. In the case where water is used as working fluid, the filling ratio should be between 20 percent and 33.8 percent. To reduce the heat pipe thermal resistance, the optimal ratio between condenser area and evaporator area should be around 0.2.