The temperature of optical fiber link is an important factor affecting the accuracy of optical fiber time synchronization, but the real-time temperature of fiber core has some problems, such as difficult measurement, large estimation error, and so on. A new method of real-time temperature measurement for optical fiber link is proposed. Through the accurate measurement of the round-trip delay sum of the optical fiber link, and filtering the delay jitter and system noise by Kalman filtering, the real-time equivalent average temperature of the fiber core of the optical fiber link can be accurately calculated. The simulation results based on the segmented temperature model verify the feasibility of proposed equivalent average temperature for the time synchronization system. The temperature control box experimental results show that the accuracy of the proposed method is about 0.015 ℃. Using the proposed method to track the core temperature in real time can improve the timing accuracy of the loopback time synchronization system by about 1 ns.