1. A method implemented in a Software Defined Networking (SDN) network, wherein the SDN network contains at least a SDN controller to coordinate traffic forwarding and at least a forwarding element to forward traffic, wherein the SDN network utilizes a plurality of flow tables to perform lookup for forwarding traffic at the forwarding element, the method comprising: determining dependency of flow tables within the forwarding element using a set of one or more dependency determination rules; constructing a dependency graph based on determined dependency of flow tables; determining a dependency degree count for each flow table within the forwarding element based on the dependency graph; and forming a plurality of parallel lookup groups (PLGs) for the forwarding element based on the dependency degree count for each flow table, wherein each PLG contains one or more flow tables, and wherein the one or more flow tables of each PLG has a same dependency degree count.