Filling phase change capsules in a container to form a packed bed heat storage unit is a typical applica-tion of phase change capsules. Phase change capsules are usually stacked in a specific layout in the packed bed flow channel. Studying the heat storage and release characteristics of a single phase change capsule in a packed bed flow channel can help optimize the design of a medium-temperature phase change heat stor-age system. Therefore, in this paper, a two-dimensional packed bed numerical model of phase change cap-sules is established. The heat transfer and flow characteristics of the external heat transfer fluid flowing through the phase change capsules in the direction of gravity, counter gravity and vertical gravity are compared and studied. The effects of flow rate, temperature and capsule diameter on the melting process of phase change capsules are studied. The results show that the heat transfer rate of the windward side of the phase change capsule in the packed bed channel is faster. Due to the thermal resistance of the cavity air and the natural convection, the complete solidification time is the shortest when the heat transfer fluid flows countercurrently. Compared with the downstream flow, the complete solidification time of the up-stream flow is shortened by 8.9 %. When the diameter of the phase change capsule is 12 mm, the melting speed of the phase change capsule with PTFE as the wall material in the center is 1.45 % slower than that of the 304 stainless steel phase change capsule, and the average heat storage rate is 1.5 % lower. The melt-ing rate of the phase change capsule with modified PTFE as the wall material cavity in the center is 6.9 % faster than that of the 304 stainless steel phase change capsule, and the average heat storage rate is 5.8 % higher. Increasing the HTF inlet velocity and temperature can increase the average heat storage rate of the phase change capsule and shorten the melting time of the phase change capsule. The heat storage and release characteristics of the capsule have important guiding significance for the design optimization and practical application of the capsule monomer and the medium temperature phase change heat storage sys-tem.