Abstract: The present disclosure provides a heat dissipation device of an energy storage system and a heat dissipation method for an energy storage system, wherein the heat dissipation device comprises: a housing, wherein at least one frame is provided in the housing, the energy storage system is placed in the at least one frame, a curved-surface guide plate is provided on the top of the at least one frame, at least one air conditioner is hung outside the housing, a cold air outlet of each air conditioner is connected to the curved-surface guide plate; a guide cavity is formed between a concave surface of the curved-surface guide plate and the at least one frame, a spreader plate is provided in the guide cavity, and the spreader plate is configured to adjust a flow direction of gas in the guide cavity.