Based on the method of phase conjugation stabilization, a real-time noise cancellation system was proposed. The system which is a modular structure, is composed of microwave reference signal generating, phase compensation and optical fiber transmission module. The experimental results of our ultra-stable 9.2 GHz frequency transfer via a 50 km fiber spool were shown. In 9 days laboratry measurement, the system exhibits frequency transfer stabilities (standard Allan deviation) of 4.2E－13@1s/4.3E－14@1day for freE－running and 5.8E－14@1s/1.9E－17@1day for noisE－compensated link. This system match the requirement of 100 km scale frequency transfer of ultra-stable microwave atomic clocks.