In order to solve the problem of low accuracy of long?distance transmission in fiber optic time transfer system, the basic principles and technical characteristics of four mainstream high?precision fiber optic time transfer methods, namely round?trip, dual?fiber bidirectional time synchronization, bidirectional wavelength division multiplexing and bidirectional time division multiplexing, were analyzed. Based on this, a single?channel time?frequency transmission device was developed. The device adopts the electrical phase compensation method to realize frequency transfer synchronization, and uses the round?trip method combined with bidirectional time division multiplexing to achieve time transfer synchronization. It uses 1 PPS and 100 MHz to jointly mark the time signal, with 1 PPS as the coarse time marker and 100 MHz as the fine time marker, to achieve high precision time synchronization. Experiments show that the uncertainty of the single?channel time?frequency transmission device is about 13 ps, which can meet the requirements of the existing fiber optic time?frequency synchronization network metrology calibration. The device has broad application prospects in the fields such as cascaded time transfer synchronization and fiber optic time?frequency synchronization network metrology calibration. It provides an important technical support for the construction of high stability, high reliability and high precision time service system.