Abstract: Energy storage is an effective measure to promote the consumption of renewable energy and improve the stability and flexibility of power system. The strategy of energy storage participating in the electricity market is extremely complex, which has become one of the key issues for the commercial application of energy storage. With uncertain electricity prices in day-ahead and real-time electricity markets, this paper proposes an optimal bidding strategy of energy storage considering cycle loss cost. In order to weigh the increasing profit of electricity sales and loss cost after multiple energy storage cycles, the impact of its cycle loss cost is considered when formulating the energy storage bidding strategy. And the impact of battery charging and discharging depth on cycle loss cost and profit is fully considered. In day-ahead market, an electricity price-quantity bidding model is established to bid for electricity price and electricity quantity simultaneously to fully consider the uncertainty of electricity price. In real-time market, the electricity quantity bidding model is established to revise and amend the bidding in day-ahead market, so that the bidding strategy is more reasonable and optimal. Case studies verify the effectiveness of the proposed energy storage bidding strategy, and indicate that the model can determine the optimal battery charging and discharging depth.