The noise of receiving end in mobile communication systems will change after the introduction of fiber optic repeater station. Through the analysis of the noise transmission distance between the fiber optic repeater and the noise change of the receiving end after introduction of fiber optic repeater station, it was found that the noise increment was mainly decided by repeater gain and the path loss from repeater to base station transmitter. Further, it was deduced that the fiber optic repeater uplink gain should be smaller than loss path by 8 dB, and its downstream gain should be designed to fully take into account the balance of the system up and down the line. Finally, a set of fiber optic repeater were designed with the system noise figure of 3 dB, uplink gain of 30 dB, and downlink power of 36 dBm. After actual delivery, it was found that the proportion of the network blind reduced to 3.18%, indicating that the repeater has quite remarkable effect, stable performance, and good compatibility with the original base.