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The asynchronous induction linear motor (AILM) is the key part in the asynchronous induction coil launcher, and a multisegment primary block feeding AILM is investigated in this paper. The phase unbalance characteristics of a traditional linear motor could be ignored when the poles are six or more; however, due to the existence of long unexcited primary between the entry and exit end of AILM with multisegment primary, the static longitudinal end effect is significantly different compared with a traditional linear motor. Through many experiments, a phenomenon has been found that the AILM had unbalanced mutual inductances, where Lac = Lbc = kLab, and the scale of k is from 1.57 to 6.25, which depends on the length of the unexcited primary. Under balanced terminal voltage conditions, the phase current shows serious unbalance in the prototype machine. It may bring much difficulty to the control system. Based on the unbalanced phenomenon and discipline of mutual inductances, the unbalance mechanism is analyzed by electromagnetic field theory and Ansoft software. The influence of the thrust, yoke field, and parameters because of this kind of unbalance is presented. The experimental results show a good agreement with the theory analysis. It provides a new way for the design and implementation of this kind of machine in the future.