A method and a system for implementing a digital signature in a mobile operating system. The method comprises: an application program coding to-be-signed data to obtain a first data packet; calling a preset system function by using an address character string of a service program, an address character string of an application program and the first data packet as parameters; when the service program is called by the preset system function, parsing function parameters, and storing the address character string of the service program; decoding the first data packet; if the decoding succeeds, sending the to-be-signed data and a preset signature type to an intelligent key device; otherwise, using decoding failure information as a returned value, and calling the preset system function by using the address character string of the application program and the returned value as parameters; receiving information returned by the intelligent key device; calling the preset system function by using the information returned b
