A method for authenticating a Short Message (SM) calling party, including: if a Signal Relay Function for support of Mobile Number Portability (MNP-SRF) module detects a calling party number carried in an SM belongs to its serving network after receiving a Mobile Originated (MO) SM, the MNP_SRF module adds an identifier of the MNP_SRF module's network to the calling party number. A Short Message Serving Center (SMSC) determines whether the SM passes calling party authentication according to the fact that whether the calling party number carries an identifier of the SMSC's network. The invention provides a system for authenticating an SM calling party, including: a Mobile Switching Center (MSC), a calling MNP_SRF module, a Number Portability Database (NPDB) and a Short Message Serving Center (SMSC). The invention may avoid a mobile number having subscribed to a new network from using resources of the SMSC of a network to which the subscription has been canceled.