In order to deal with the Software Defined Network(SDN) load balancing problem, the traditional ant colony algorithm is improved and a joint algorithm is proposed by combining with the server load balancing algorithm. In the proposed method, the weighted least connection scheduling algorithm(server side) is employed, and the server with the least load is selected; the Improved Ant Colony algorithm(Im-ACO) is adopted to find the optimal path to the selected server. Theoretical analysis and experimental results show that the proposed joint algorithm significantly improves the network performance with higher network throughput and lower packet loss rate.