Abstract: Blockchain has received a lot of attention in recent years, and the digital signature scheme is a legitimate way to authenticate transactions in the blockchain. The threshold signature scheme enables the key controlled by a single participant to be managed by multiple participants at the same time, and the transaction can be signed only if more than a threshold number of participants sign at the same time, which expands the application mode and application scenario of cryptocurrency, and reduces the risk of single point of failure. However, existing threshold signature schemes are mostly limited to traditional public key signature algorithms such as ECDSA (elliptic curve digital signature algorithm), which incur significant overhead in public key certificate storage and management. IBC (identity-based cryptosystem) can effectively address this issue, but there is no corresponding research on threshold SM9 signature schemes. Implementing a threshold signature scheme usually requires the use of a two-party secret sharing conversion protocol. To address the low efficiency of the existing two-party secret sharing conversion protocol based on the Paillier encryption algorithm, we propose a two-party secret sharing conversion protocol based on the ElGamal encryption algorithm, and apply it to construct a threshold signature scheme based on SM9. In addition, in order to prove the security of the scheme, an identity-based threshold signature ideal function is constructed, and the security of the scheme is proved under the UC (universally composable) model. Theoretical analysis and experimental results show that the threshold SM9 signature scheme based on the ElGamal algorithm is more efficient than the existing schemes. In particular, when the threshold is 100, the speed is about 6.1 times that of the Paillier-based scheme. The threshold signature scheme is tested on three different blockchain platforms, Ethereum, Hyperledger Fabric and ChainMaker on Tencent blockchain as a service. The experimental results show that the scheme is feasible in the blockchain scenario.