The present invention discloses a method for implementing a real-time data service, a real-time data service system and a mobile terminal. Said method for implementing a real-time data service includes the following steps: before encapsulating a Media Access Control Protocol Data Unit (MPDU), a Wireless Local Area Network Privacy Infrastructure (WPI) module in an Access Point (AP) needs to determine the type of the data to be encapsulated in the MPDU; if the data is a control signalling message of a real-time data service, the WPI module encrypts said data, then encapsulates the encrypted data in a data (e.g. PDU) field of the MPDU, and transmits the encapsulated data to the mobile terminal; if the data is an audio/video data message of a real-time data service, the data is not to be encrypted, but is encapsulated directly into the data (e.g. PDU) field of the MPDU in plaintext, and then transmitted to the mobile terminal. The present invention can reduce the processing load and the software and hardware costs of the AP and the mobile terminal.