The development of latent heat storage technology is conducive to the large-scale application of renewable energy. However, the low thermal conductivity of its thermal medium delays the performance of heat storage and release. In this paper, the effect of inclination angle and gravity on the melting performance of the phase-change thermal storage vessel was studied by combining experiment and numerical simulation, and the factors such as phase interface, melting rate, and heat storage are further analyzed. The results show that the decrease in gravity weakens the natural convection and reduces the heat storage capacity. Under the same gravity condition, with the increase of inclination angle, the melting speed of the system gradually decreases, but the heat storage gradually increases. The average temperature uniformity shows that the decrease in gravity makes the heat transfer more uniform. Compared with 1 g, the average temperature uniformity under 0 g is increased by 41.77 %, and the temperature uniformity is the best when the inclination is 60°.