RF photonic link can provide significant benefits in transmitting and distributing RF signals to many separating stations by optical fiber. However, phase noise of transmitted RF signal in electrical-optical-electrical conversions is generally deteriorated by related optical noise. In this paper, a theoretical model about phase noise of RF photonic link is built, and the expressions and characteristics about phase noise are investigated. In the RF photonic link, phase noise is investigated for 100MHz RF signal. The experimental results can agree with the theoretical analysis.