The characteristics of two types of Optoelectronic Oscillators (OEOs) based on phase-locked loop technique and injection-locked technique were analyzed and compared. The noise transfer functions of the two types of OEOs were deduced and verified by experiments. The similarities and the respective merits between the two techniques were discussed. There is a problem of losing lock in the two types of OEOs because the optical fiber has a high sensitivity to temperature. To solve this problem, a locking state monitoring and feedback system was designed according to the phase difference between the output signal and the reference signal. The system was also verified by experiments.