The characteristics of fiber loop have important effect on the performance of the phase locking array of fiber lasers based on a common fiber loop. The configuration, properties of the array and the functions of the loop are introduced. The theoretical model of the loop is established, and its power transmission and resonance properties are analyzed by the intensity and amplitude addition methods respectively. It is proved that they are consistent when the line-width of input light-wave is considered. The research results indicate that increasing the fiber coupler's coupling ratio can increase the coupling strength among component lasers of the phase locking array, and the output power and combining efficiency will not decrease obviously if the loop's loss is low. The filtering effect of fiber loop is observed in experiment, and the output power decreases slightly and regularly with the increase of coupling ratio, which is consistent with the conclusions obtained from theoretical analysis.