Dynamic voltage scaling is an effective low-power technique. Using the technique, compiler-directed dynamic voltage scaling can reduce computer’s energy consumption effectively. Based on programming language’s syntax tree, a real-time dynamic voltage scaling algorithm for low power is presented, and the algorithm assisted with static timing analysis could make intra-task dynamic voltage scaling by automatically inserting dynamic voltage scaling source code. The algorithm has been realized in the real-time low-power system RTLPower, and obtained energy reduction of up to 50 percent over no power management in some real-time embedded benchmarks.