Abstract: Magnetism that the alkaline battery carries disturbs the majority of precision instruments and then affects the data acquisition. This article, based on the battery composition structure and the characteristic of manufacturing technique, discovered the two major causes in battery magnetizing that the metallographic phase transformation happened in cold rolling and punching on battery metal shell and the magnetization from magnetic field in the assembly line. Through studying on degaussing methods and massive experiments, a method named saturated magnetizing first and then 50Hz degaussing was developed. After three times of degaussing, 100% of battery samples have been achieved the goal that residual magnetism Br 0.2 mT.