Provided are a method and system for backing up the private key of an electronic signature token, the method comprising: a first electronic signature token transmits a private key backup request data packet comprising a first signature; a second electronic signature token authenticates the first signature in the private key backup request data packet; if the first signature passes authentication, then determining whether the first electronic signature token has a backup relationship with the second electronic signature token; if yes, then encrypting the private key of the second electronic signature token, and transmitting a private key backup response data packet comprising a second signature and the encrypted private key; the first electronic signature token authenticates the second signature in the private key backup response data packet; if the second signature passes authentication, then determining whether the second electronic signature token has a primary-standby relationship with the first electronic signature token; and if yes, then decrypting the encrypted private key.