With the development of web service applications, QoS becomes a severe problem. By using the average response time as the performance metric, a way about web se rvices differentiated QoS is verified and then a method to model target response time is proposed. Meanwhile, an efficient method is proposed to solve dynamic p rogramming questions. A prototype system is designed and implemented in the web service runtime environment. Experimental results show that this method is effec tive to control workload balance and provide web service differentiation.