<p>Multistage latent heat thermal energy storage systems (LHTESS) are an efficient way of storing and utilizing thermal energy due to their faster heat storage and heat release rates and more uniform heat transfer fluid (HTF) outlet temperatures compared to a single-stage system. This paper proposed a three-stage LHTESS filled with phase change material (PCM) in the tube, and constructed the numerical simulation model for comparing the heat storage performance with different placement configurations and highlighting the differences between the proposed system and single-stage LHTESS. Meanwhile, the variations in melting characteristics the heat release performance are analyzed by field synergy theory. The results show that the differences in melting performance of the PCM at each stage in the vertical three-stage LHTESS are greater compared to the single-stage PCM than those observed in the horizontal system. In the horizontal three-stage LHTESS, compared to the vertical system, the complete melting time of the PCM at each stage reduces by 32.1%, 34.3%, and 35.9%, respectively. Meanwhile, the solidification time also reduces by 8.2%, 9.5%, and 7.9%, respectively. Based on the field synergy theory, horizontally placed PCMs at each stage have more intense natural convection and better synergy between velocity gradient and temperature gradient. The horizontal device has an average increase of 15.8% in the synergy angle of each PCM compared to the vertical device, and it has a better heat transfer enhancement effect. This provides a new idea for the design and research of latent heat storage systems.</p>