Abstract: According to features of coal mine such as narrow tunnel,more turning points and more branches,a design scheme of fiber-optic repeater system in mine based on DSP was proposed for the questions such as poor quality of mobile calls and low reliability of mobile communication system in underground environment.Designs of automatic monitoring and control unit based on DSP and FIR digital filter and application of voice activation technology in repeater system were introduced in details.The fiber-optic repeater system solves the difficulty of mobile communications in wide range in mine and uses DSP to monitor the system automatically to make the system stable.The application of digital filter and voice activation technology makes the underground communication system more stable in performance,better in voice quality and stronger in anti-interference.The system establishes a basis for best working of mobile communications in mine.