In the region of maneuvering target tracking, the traditional interacting multiple model algorithm has a fixed structure, which brings unnecessary inter-competition among the amount of models and calculation burden that the algorithm needs enough models to ensure the accuracy. To resolve this contradiction, a variable structure multiple-model algorithm based on digraph switching and unscented Kalman filter is presented. According to the target motion state basis at different times, the algorithm can match sub-model-set based on the digraph. Simulation results show that this algorithm improves the accuracy of tracking by reducing the competition of the models as well as reducing the computation burden.