Sharing energy storage (SES) is a novel business model in order to increase the profits and improve the utilization rate of idle energy storage facilities. On the other hand, blockchains can be competently applied in the transaction and operation of SES because of distributed network architecture, traceability and tamper proof. In this paper, a management model of SES based on proxy signatures in the blockchain environment is proposed. Many management models including the principal-agent model are analyzed for SES in terms of benefit, cost, resources, and so on. Moreover, a blockchain framework and a typical transaction process of SES is presented. Finally, a proxy signature mechanism based on the ElGamal algorithm is proposed in order to address the problem that the signature power of nodes cannot be transferred on blockchains. Simulation results show that the proposed proxy signature mechanism can achieve the delegation of digital signature power under the premise of security and reliability, which is suitable for the management model of SES on blockchains.