The influence of backscattering and injected signal on the statistical properties of ring lasers is discussed by a full saturation laser theory. The result shows that the backscattering can reduced the fluctuations of the system. For a homogeneously broadened bidirectional ring laser, the injected signal can drive the weak mode from incoherent light to coherent light. However there is no such driving effect in an inhomogeneously broadened ring laser system. Further study shows that the driving effect of the injected signal also depends on the difference of pump parameters Δ α of the two modes.