This paper investigates the precise measurement of the time-delay lines. Firstly, the error of traditional group delay measurement is introduced and the mechanism of error formation is analyzed, and then propose the time delay accurate measurement based on the combination of group delay and phase delay. The method adopts the secondary measurement, combined with the coarse measurement of group delay and the accurate measurement of phase delay, to complete the accurate measurement of time delay. We verify that the proposed method has higher measurement accuracy in delay measurement through simulation and experiment.