The invention discloses a universal digital signature method for a Web application system. The universal digital signature method comprises the following steps that 1.1, a user applies for a key through a digital signature system; 1.2, the digital signature system background allocates a key pair to the user, encrypts a private key into a private key ciphertext, and generates a key signature; 1.3,the user signs on the signature page of the application system; 1.4, the digital signature system background takes out the private key ciphertext from a digital signature database, decrypts the private key ciphertext to obtain the private key of the user, and signs the data needing to be signed by using the private key; 1.5, the application system signature page subjected to digital signature displays a signature needing to be verified; 1.6, the digital signature system background takes out the public key of the user from the digital signature database, verifies a signature result, and feeds back a signature verification result to the application system signature page; and 1.7, the application system signature page displays the signature verification result. The method is suitable for various operating systems and browsers, good in compatibility, beneficial to popularization and application and capable of being widely applied to Web application systems.