Small signal perturbation method is usually used for the automatic bias control of electro-optic modulator.This method is mainly applied in high speed digital communication,but is not suitable for the transmission of analog signals.An iterative algorithm is proposed,which can lock the best bias point based on closed-loop control method.The feasibility of this method is analyzed in theory,and the feedback system is built.Experiment is carried out under condition of varying temperature.The result shows that the output power jitter is less than 1.5% as the temperature change rate is less than 5 ℃/min.This method can be used in the transmission of analog signals.