High-precision and high-stability time-frequency signal transmission is a reliable guarantee for the normal operation of on-orbit satellites. The transmission link bandwidth of time-frequency transmission system using redundant coding method is above Gb/s level. In this paper, a new time-frequency transmission system is designed, which optimizes the encoding and decoding methods with limited bandwidth, and achieves high-precision transmission of frequency standard signals under the bandwidth of 5 MHz link. The high precision transmission of time-frequency is realized by microwave photon fusion. The results showed that the time jitter of the time-frequency transmission system reached 1.65 ns and the frequency stability of 1.39×10-11/s and 3.45×10-12/(10 s).