The invention discloses a digital signature method for escrowing the private key of a mobile terminal. The mobile terminal needs to provide digital signature service in the development of e-government application, however, at present, the mobile terminal is lack of a safety condition providing a private key saving digital signature, the private key is likely to be stolen by a hacker at the mobile terminal, so that the digital signature cannot be realized directly by the mobile terminal. The invention provides a digital signature technology for the mobile terminal. The digital signature technology comprises the mobile terminal, a signature server and a KMC server cipher machine. The signature server is responsible for managing the signature private key of the user, all private keys of the system are encrypted and then saved in the cipher machine, the encrypted user' private key is mastered by the user, and the cipher machine is only communicated with the signature server. When a certificate is downloaded by a user, the terminal application packs a Hash value in digital signature and user identity information together to form digital signature request message, the digital signature request message is sent to the signature server through a short message, after the user request validation is passed, the cipher machine is called, and after the user' private key is digitally signed, the result is returned to the user to complete the digital signature process.