Previous studies in literatures adequately emphasized that inserting fins into phase change material is among the most promising techniques to augment thermal performance of shell-and-tube latent heat thermal energy storage unit. In this study, the novel unequal-length fins are designed from the perspective of synergistic benefits of heat transfer and energy storage performance, and the effects of arrangement, number and total length of unequal-length fins are numerically investigated. Results show that utilization of fins with ascending length, when short and long fins are located in the inlet and outlet of heat transfer fluid respectively, can further promote the heat transfer and energy storage performance compared with equal length fins, and a maximum 6.17% and 0.43% increment of heat transfer performance and stored energy is achieved in full melting time, respectively. The number of unequal-length fins plays a major role in the energy storage, and 18.95% and 0.91% improvement of heat transfer performance and stored energy is realized when equipped with 2 unequal-length fins. A 21.17% improvement of the heat transfer performance is obtained when the total length of unequal-length fins is 18 mm. The present study is helpful to make further efforts to enhance heat transfer and energy storage of shell-and-tube latent heat thermal energy storage unit with unequal-length fins.