The invention relates to a method for on-line estimation of internal resistance of a power lithium battery. The method for on-line estimation of the internal resistance of the power lithium battery comprises the steps that an automobile is energized to travel, and a battery management system obtains the working condition of the automobile in real time; a current changing curve graph with the working condition same as or close to the real-time traveling working condition of the automobile is selected according to the real-time traveling working condition of the automobile; the maximum current value I1 and the minimum current value I2 in the current changing curve graph are selected; in the process of traveling discharging process of the automobile, when the current value at present is equal to the maximum current value I1, the battery voltage value at the moment is recorded as the minimum voltage value U2; when the current value at present is equal to the minimum current value I2, the battery voltage value at the moment is recorded as the maximum voltage value U1; the formula R=(U1-U2)/(I1-I2) is used for calculating the battery direct-current resistance R. Compared with the prior art, an auxiliary device or other externally-connected measuring devices are not needed, internal resistance value of the power battery can be estimated in an on-line mode in the traveling process of the automobile, the method is used only according to real-time battery voltage data and real-time battery current data in the traveling process of the automobile, and the method is simple, easy to implement, practical, and easy to popularize and use.