How to effectively allocate system resource to meet the Service Level Agreement (SLA) of Web servers is a challenging problem. In this paper, we propose an improved scheme for autonomous timing performance control in Web servers under highly dynamic traffic loads. We devise a novel delay regulation technique called Queue Length Model Based Feedback Control utilizing server internal state information to reduce response time variance in presence of bursty traffic. Both simulation and experimental studies using synthesized workloads and real-world Web traces demonstrate the effectiveness of the proposed approach.