The WIA-PA standard is developed for process automation in industrial wireless network by China. In WIA-PA, the wireless resources include the channel and time slot resources for intra-cluster and inter-cluster communication. In order to meet the requirements of the high interference resistance, low-latency and high reliability in industrial network communication, it adopts frequency hopping communication mechanism and TDMA access mode. In this paper, we focus on the strategy of inter-cluster communication resources assignment. The problem can be translated to graph coloring and solved by the algorithm based on Set Theory. Experimental results show that the algorithm plays a good performance in the channel and time slot resources allocation.