Abstract: The heat pipe cooled reactor has become the current key development route because of its good inherent safety characteristics and modular design concept. As one of the important components of the reactor, the safe operation of the alkali metal heat pipe is essential. However, the geyser boiling phenomenon in the heat pipe will cause a lot of vibration in the heat pipe, which will lead to the rupture of the heat pipe in severe cases. At present, there are few published research results on the geyser boiling experiment of alkali metal heat pipes, and the influence of different parameters on the geyser boiling phenomenon is not fully evaluated. Therefore, in this paper, sodium metal heat pipes were used to carry out geyser boiling experiments and research on mechanisms. The experiment was carried out with heating power of 150-1 300 W, inclination angle of 45º-90º and condensing section length of 50-60 cm. The effects of heating power, inclination angle and cooling capacity on geyser boiling were analyzed. The results show that when the length of the condensing section is 60 cm and the inclination angle of the heat pipe is 60°-90°, the period and amplitude of geyser boiling decrease with the increase of heating power. In vertical working conditions, the average period is 736.4 s and the temperature amplitude is 55 ℃ when the power is 450 W. After the heating power gradually increases to 500, 550 and 600 W, the geyser boiling period drops to 70.2, 32.9 and 28.1 s, and the amplitude of geyser boiling decreases to 27.2, 17.2 and 16.6 ℃, respectively. However, the influence of power on the geyser boiling of sodium heat pipe is not single, and it shows different rules when the inclination angle is 45°. In the experimental range, the power range of geyser boiling is advanced and the intensity of geyser boiling increases with inclination angle. The overall intensity of geyser boiling is the highest at 90º, and the temperature oscillation period and amplitude are 8.8-666.7 s and 0.5-60.3 ℃, respectively. The cooling capacity affects the intensity and power range of geyser boiling. Geyser boiling is more likely to occur and has higher intensity when the cooling capacity is strong. The research results of this paper can provide a reference for the optimization of operating conditions for heat pipe cooled reactors.