Due to the huge routing algorithm search space for 2D mesh based Network-on-Chip (NoC), Divide-Conquer method is presented to effectively explore the search space. When using Divide-Conquer method, a large number of routing algorithms will be created. In order to get the final results in an acceptable time, a precise metric is needed to measure routing performance and discard the poor performance routings. In this paper, we propose a new routing performance metric, namely, network pressure. Network pressure has the following three advantages: (1) it could measure the whole network congestion state; (2) network pressure of a network and that of its partial component is highly related, under the same routing; (3) it is closely related with routing performance. Based on network pressure and Divide-Conquer method, high performance routing could be achieved. The obtained routing is called suboptimal routing due to the following two reasons: (1) there is only a little gap between its performance and that of the fully adaptive routings under both transpose1 and transpose2 traffics. (2) the search space of routing algorithms is systematically and widely exploited.