Interactive systems with dynamic tasks have been widely used recently. In this study, a computational interaction model ICOM^DT for dynamic tasks is proposed based on the existing research, which is used to describe interactive processes and predict user's intention. More specifically, ICOM^DT is applied to moving target selection, and two experiments are designed to verify the validity of the model. In the first experiment, user data is collected to fit the model and predict error rates. Results show that the proposed model fits the empirical data well and the predicted value is also close to the true value. In the second experiment, an assistant moving target selection technique ICOMPointer is achieved. By comparing with the basic selection technique and the other two state-of-the-art selection techniques in a game, it is found that ICOMPointer performs well. The ICOM^DT model is of great significance for computer to understand user's intentions and improve the efficiency of interaction between users and dynamic tasks.