Based on quantum one-time pad and quantum key distribution, a quantum sequential multi-signature protocol of classic message is proposed. Different from known quantum sequential multi-signature protocols, the signature can be accomplished only by unitary operation of single photon instead of multi-particle entangled states. The protocol has high flexibility, and it is easy to implement the addition and deletion of the signer. Security of the protocol proposed mainly depends on the unconditional security of quantum key distribution. The existing various attacks on this agreement is also invalid. Compared with other well-known quantum sequential multi-signature protocols, efficiency of the protocol signature and verification process is greatly improved.