The development of mobile communication technology has become a dazzling star in the information field. Especially for the third-generation mobile communication, Mobile phone Bluetooth is a highly-anticipated technology, with wide application prospects and potential economic value. Bluetooth mobile phone is incredibly good at connecting wirelessly to other terminal equipments and transferring data between devices very near each other. Meanwhile, the security of mobile phone Bluetooth transmission becomes the concern of the current users, and ensuring the security of Mobile phone Bluetooth transmission is also a problem to be solved urgently. In this paper, the file transport mechanism of Mobile phone Bluetooth is the main research object. Based on link protocol, using the security analysis of link connection mechanism, this paper improved the Personal Identification Number (PIN) input from the user interface, in order to enhancing the security of link connection mechanism of the underlying file transfer protocol