Like traditional server farm, DHT-based server farm has high requirement on load balancing. Traditional solutions to balance load in DHTs either can not satisfy the requirement of server farm, or incur a high overhead. This paper presents a novel load balancing algorithm designed for server farm. Compared with the traditional virtual nodes algorithm, our algorithm generates the virtual IDs in the optimal intervals. This method has lower overhead than traditional methods, and can achieve a high load balance among the nodes. Moreover, with considering the load of backup data, which usually ignored in other methods, our algorithm can be used well in the real system.