Scalable Video Coding (SVC) makes it possible to change video quality dynamically according to real-time bandwidth. For quality control algorithms of SVC video streaming, the biggest challenge is to keep a video quality that is both smooth and as good as possible. In this paper, we first introduce a combined quality level scheme to describe SVC video quality in a unified way. Then an effective and efficient quality control algorithm for SVC video streaming is proposed based on the Proportional-Integral-Derivative (PID) control method. Extensive experiments show that the proposed algorithm improves 8.6% in video quality with 24.8% reduction in quality fluctuation compared with the existing packet delay feedback algorithm. The proposed algorithm has also been implemented in online video website www.7dlive.com and performs well in applications.