With the development of the wireless handsets and 3G wireless networks, the demands of multimedia messaging service becomes increasingly important and the service is expected to be one of major services in the wireless communication systems. However, sending and receiving multimedia messages through the mobile phone have their faults. For making use of the PC's handling ability, this paper proposes the design method of a mobile multimedia messaging service (MMS) system. Connected a PC with a mobile phone through a serial port or a USB port, used VC++6.0 as the development platform, and based on windows serial communication, database programming of ADO smart pointers etc., the system is designed and implemented. In order to improve the sending efficiency and real-time performance of MMS, a MMS message real-time parallel sending algorithm based on multithreading is proposed.