The invention relates to a lithium ion battery electrochemical impedance online monitoring testing method. With the method adopted, the technical problem that an existing testing method cannot complete electrochemical impedance testing online can be solved. The method of the invention includes the following steps that: S100, a battery to be tested is arranged in a constant-temperature cabinet, andthe battery to be tested is charged to be in a certain SOC; S200, electrochemical impedance spectroscopy (EIS) testing is performed on the battery to be tested, and impedance values generated by eachpolarization are obtained through analysis; 300, the battery which has been subjected to the EIS testing is connected with a high-precision test cabinet, and current pulses of different gradients areapplied to the battery; and S400, the pending voltage of the battery before the pulse of certain pulse current I is recorded as U0, and the voltage of the battery after a pulse t 2 is recorded as Ut,and deltaU=U0-Ut, and deltaU and pulse current I under different pulse current are selected, so that graphing can be performed, linear fitting is performed, and a slope, namely the impedance value ofDCR testing, is obtained. According to the method of the invention, a direct current method and an alternating current method are combined; the on-line monitoring of the electrochemical impedance change of the battery can be realized through the direct-current impedance test of small-rate current pulses. The method has the advantages of simple experimental process and high practicability.