Node - state information is an important factor in QoS research. The Probability Mass Function (PMF) of delay at each node is taken as state information and a filter algorithm is proposed and used for normalizing it. And the simulation proves that the PMF is still a normal distribution function through scheduler. Experimental results and theoretical analysis show that the method is effective and feasible in simplifying the network calculation and improving the stability of node - state to meet the corresponding statistical guarantees.