The precise measurement of time and frequency, which has the smallest uncertainty (10^-15~10^-18) of all types of measurement, is of great interest for a wide range of applications including basic science, metrology, broadband communication networks and navigation with the Global Positioning Systems (GPS). The recent development of optical frequency measurement based on femtosecond combs has stimulated the field of frequency metrology, especially research on optical frequency standards. One major challenge for scientists working on high-precision frequency standards and measurements is to deliver and compare state-of-the-art clocks at different locations. Here we demonstrate a precise frequency measurement over a physical distance of 50 km between Tokyo and Tsukuba using a phase-stabilized 120 km optical fiber link and coherent optical transfer. The transition frequency of the strontium optical lattice clock at the University of Tokyo is measured to be 429228004229874.1(2.4) Hz. The results demonstrate the excellent functions of the intercity optical fiber link, and the clear potential of optical lattice clocks for use in the redefinition of the second.