The invention discloses an electronic contract signing system based on a mobile phone client. The system comprises the mobile phone client and a service end. The mobile phone client is in wireless communicating connection with the service end. The service end comprises a contract management and storage module, a member automatic customization module, a contract creating module, a contact editing module, a signing module, a stamping module, an invitation module, a contract enclosure module, a sharing module and the like. The system further comprises a recording module, a negotiation chamber module and the like. According to the invention, individual users and unit users are separate through the member automatic customization module, units can have administrator accounts simply through registration once, employees do not have to perform registration individually, all the employees can use the system individually and sign contracts with clients independently, and through implementation of a "signing/stamping+recording" dual-guarantee mechanism, fake signing is prevented; and after the contracts are signed, the contracts are enclosed, locked and are automatically stored in a fragmentation manner, and thus security is ensured.