Abstract: The liquid alkali metal is one of the coolant materials for space nuclear reactor, and its thermophysical parameters are an essential basis for the selection of coolant materials. The existing experimental data on the density and surface tension of liquid alkali metals are less,and the development of space reactors has higher requirements. According to the maximum bubble pressure method, an experimental device that can simultaneously measure the density and surface tension of liquid alkali metals is developed, and the reliability and availability of the device are verified with lithium with the purity of 99.9% as the measured medium. The results showed that the average deviation of the density was 0.47%, and the average variation of surface tension was 0.93%, with good linearity in the temperature range of 200℃～650℃ and under standard atmospheric pressure compared with the literature reference values. The empirical relationship between liquid lithium’s density, surface tension, and temperature is given on this basis. Finally, the effects of the tube diameter and the bubbling speed on liquid lithium density and surface tension measurement results are analyzed, and corresponding experimental suggestions are given. The work in this paper can provide a reference for the high-precision measurement of the density and surface tension of liquid alkali metals at high temperatures.