A method of high-precision harnessing of the on-board clock has been studied, which mainly consists of determining the amount of clock frequency adjustment in the mode of ground-controlled calculation or on-board autonomous calculation, based on which the time–frequency signals output from the satellite can be regulated to synchronize with the ground standard time. Taking the analog high-precision clock maintained by the ground monitoring station as the reference signal, the time signals generated by the small rubidium clocks and high-stability crystals carried by the satellite are tested, and the feasibility of the proposed technical scheme is verified. The experimental results on the principle prototype of the designed time–frequency unit show that, after harnessing the satellite time–frequency reference source with high finesse, better accuracy and long-term stability can be obtained with minimal impact on the short-term stability of the time–frequency reference source itself. Among them, the maximum deviation between the time–frequency signal generated by the small rubidium clock and the reference signal of the ground monitoring station after harnessing is less than 0.25 ns; the peak phase error between the time–frequency signal generated by the high-stability crystal and the ground reference signal after harnessing is less than 0.8 ns.