In order to solve the technology problems in the field of power system harmonics detection and estimation, this paper attempts to combine the approximate entropy measure and the chaotic oscillator firstly. Basing on the theoretical analysis and the simulation research, this paper proved that the output approximate entropy of the adaptive-step-length intermittent chaotic oscillator is just relevant to the frequency of the signals to be detected. Furthermore this paper proposed the intermittent chaotic oscillator with the approximate entropy measurement, and described the applicability ofSthis new method to the harmonics detection. Besides improve a synchronization estimation method of the amplitude and phase, make the method complexity lower and the real-time performance better.