In Software-Defined Networking (SDN), inconsistent updates are frequent when the controller needs to update the flow table entries in multiple switches due to the change of configuration policy. The internal reason of this phenomenon is that the controller updates all switches asynchronously. Update delay leads to the logical inconsistency of the network state, affecting the correct forwarding of data messages. With regard to poor generality of application scenarios and prolonged update time of the classification and sequence based update scheme and high computational complexity of the optimal update scheme, this study proposes a Categorical Search based loop-free Consistent Update scheme (CSCU) for flow tables. In this scheme, a switch classification model is developed on the basis of classification, and a loop search optimization model is built according to the idea of node dependence. Those contributions achieve the consistent update with short update delay and high update efficiency. The simulation results show that the proposed scheme has promising applicability with lower node operation complexity as well as fewer update rounds, which can markedly improve the update performance in terms of lower computational complexity.