In the background of the joint operations of ground synthetic units, a threat assessment indicator system based on cluster targets was established. Aiming at the problem of the imbalance of state in the traditional threat assessment method caused by invariant weight, the interval number theory was introduced to determine the index interval invariant weight, and the variable weight theory was used in combination with the combat situation to determine the index interval variable weight, so that the weight can be dynamically adjusted with the change of the battlefield. By combining interval variable weight with grey correlation method, the least-squares grey-correlation threat assessment model for interval number was constructed. Finally, the effectiveness of the model and the method was verified by the example simulation.