The requirement of increasing the deployment of a distributed monitoring system as the network expanding is becoming a new research focus. The problem is where to put those monitors and by how much to put. This paper analyses the monitors adding mechanism and present a novel algorithm for finding candidate locations for additional deployment in the network. The algorithm is based on Apriori search method that combines with the link weight change algorithm. We also develop the greedy algorithm with Group Betweenness Centrality(GBC) involved for the purpose of comparing. The result shows that the new algorithm need less additional monitors than greedy algorithm, thus is useful for network monitors deployment.