The present invention discloses a method for realizing the CNAP service, including: receiving a service request sent by the switching system, where the service request carries the identifier of the calling party and the identifier of the called party; querying the calling information set by the calling party according to the identifier of the calling party, and querying the location information of the called party according to the identifier of the called party; after determining that the called MS already rings, sending a flash message that contains the calling information to the called MS according to the location information of the called party. The present invention also provides a calling information service apparatus accordingly. The invention correlates the judging of the status of the call connection process with the time of implementing the CNAP service. Therefore, the calling information can be sent to the called MS at a proper time, thus helping the called party to identify the calling party correctly.