As the portion of coupling capacitance increases in smaller process geometries, accurate coupled noise analysis is becoming more important in current design methodologies. We propose a method to determine whether aggressors can potentially switch simultaneously with the victim or not. The functional information is used to classify the aggressors. Our functional pruning algorithm inspects the conflict of the net states using CNF(Conjunction Normal Form) and BDD(Binary Decision Diagram). We present the experimental results on several industrial circuits. In the experiments, 6.4% of total aggressors are false and the accuracy of delay calculation can be improved up to 36.6%.