The technology of Radio over Fiber (ROF) not only has broad prospects in the field of communications, but also has great potential in the field of radar. ROF technology will be able to change the traditional structure of radar and radar network, improve their performance. The radar can be reduced to a system that has only transmitter, receiver, transmission line and antenna. Other equipment can be concentrated to the command center. The command center will be not only a data processing center, but also a signal processing center. At first, this paper analyzed the factors that influence the phase stability of microwave signal in fiber. For a short fiber, the stress in the fiber direction is the major point that influence the phase stability, other factors can be neglected. For a long fiber, all factors should be considered. And then, this paper analyzed the technical requirements of radar signal transmission, concluded that the phase stability of ROF system is the most important factor for radar, and chosen the method of phase compensation to solve this problem. At last, this paper designed a ROF link for RF transmission of radar.