In this paper, an optical fiber time transmission technology based on a double-fiber round-trip method is provided. In the system, the one-way transmission delay from the master station to the slave station can be calculated directly through the measurement of three time interval counters and their ratio relationship. The method eliminates the influence of fiber length expansion and round-trip transmission delay fluctuation, which is caused by ambient temperature change. The master and slave stations are connected by 100 km and 80 km optical fibers, respectively, and the temperature of the optical fiber link varies from -20∘C to 40°C. Compared with the single-fiber round-trip method, the time interval error of a double-fiber round-trip method is reduced from 1.4 ns to 80 ps when the wavelength is 1310-1550 nm, and from 320 to 80 ps when the wavelength is 1490-1550 nm.