Liu, N. Arakawa, D.A. Katagiri, H. Matsumoto, T. Michizono, S. Miura, T. Qiu, F. Yano, Y. JACoW Publishing Geneva, Switzerland 978-3-95450-184-7 10.18429/JACoW-IPAC2018-THPML073 English 4815-4818 THPML073 Contribution to a conference proceedings 2018 2018-06 https://doi.org/10.18429/JACoW-IPAC2018-THPML073 http://jacow.org/ipac2018/papers/thpml073.pdf The SuperKEKB injector is a more than 600 m J-shaped LINAC. The requirement of the RF phase refer-ence stability is 0.1 degree (RMS) at 2856 MHz for SuperKEKB PHASE-2 commissioning. In order to clari-fy and improve the reference line performance, the RF reference phase stability is measured. The phase noise of the RF reference at each sector is shown in this paper. A new phase monitor system is implemented to measure the short-term stability and long-term drift due to the temperature and humidity fluctuations in the klystron gallery.