This paper proposes and experimentally validates a large-scale multi-antenna and one-receiver global navigation satellite system (GNSS)-over-fiber differential positioning system using silicon on-chip optical routing. The radio-over-fiber (RoF) distributed antenna architecture is utilized to facilitate remote multipoint GNSS signal acquisition, and RoF transmission links featuring low loss, large bandwidth, and immunity to electromagnetic interference are reaped to achieve the centralized reception of remotely collected GNSS signals at the local end. At this end, a complementary metal-oxide-semiconductor (CMOS)-process-compatible high-speed silicon optical switch chip is fabricated for the periodic switching and differential calculation of GNSS signals over fiber obtained at different monitoring points. Then, a time-division multiplexing-based multi-antenna and one-receiver GNSS positioning system using on-chip optical routing is built. In the experiments, a self-developed 1×8 thermo-optic silicon optical switch chip based on a Mach-Zehnder interferometer is employed to build an experimental multi-antenna GNSS positioning system with five remote monitoring points. The RoF transmission distance of the GNSS signals is 10 km. According to the experimental results, the real-time response time of the optical switch chip module is less than 200 μs. Stable and high-accuracy positioning at five remote monitoring points (10 km away) is achieved without the aid of additional optical amplification. The obtained positioning accuracy in the east (E), north (N), and up (U) directions is all at the millimeter level.