In a data center network(DCN),load balancing is required when servers transfer data on the same path.This is necessary toavoid congestion.Load balancing is challenged by the dynamic transferral of demands and complex routing control.Because ofthe distributed nature of a traditional network,previous research on load balancing has mostly focused on improving the perfor-mance of the local network;thus,the load has not been optimally balanced across the entire network.In this paper,we propose anovel dynamic load-balancing algorithm for fat-tree.This algorithm avoids congestions to the great possible extent by searching fornon-conflicting paths in a centralized way.We implement the algorithm in the popular software-defined networking architectureand evaluate the algorithm’s performance on the Mininet platform.The results show that our algorithm has higher bisection band-width than the traditional equal-cost multi-path load-balancing algorithm and thus more effectively avoids congestion. In a data center network (DCN), load balancing is required when servers transfer data on the same path. This is necessary toavoid congestion. Load balancing is challenged by the dynamic transferral of demands and complex routing control. Abstract of the distributed nature of a traditional network, previous research on load balancing has mostly focused on improving the perfor-mance of the local network; thus, the load has not been optimally balanced across the entire network. In this paper, we propose anovel dynamic load-balancing algorithm for fat- tree. This algorithm avoids congestions to the great possible extent by searching for non-conflicting paths in a centralized way. We implement the algorithm in the popular software-defined networking architecture and evaluate the algorithm’s performance on the Mininet platform. The results show that our algorithm has higher bisection band-width than the traditional equal-cost multi-path load-balancing algorithm and thus more avoidance congestion.