Nowadays, power quality detecting devices have some problems in the applications. The low cost and the multi-function have been the main contradiction. For these, this paper designs a dual-core power quality detecting system based on the latest TI's OMAP-L138 chip, which has both ARM and DSP core. With the high-speed ADS8556 chip, the system achieves real-time data acquisition, processing and analysis. The hardware design makes the system highly integrated, lower cost and easy to be integrated into enterprise information management system. The windowed fast flourier transformation is adopted to detect harmonic, and S-Transform is used to detect interferences automatically and quickly, wavelet transform and binary tree support vector machine are also used to make interference classifications. Experiment results show that this design meets the requirements and different algorithms make the system more automatic and intelligent, it can reduce labor costs significantly. The system with low cost and the multi-function is better than others.