Three-phase circuit instantaneous reactive power theory has received a successful application in detecting harmonic and reactive current timely, the ip-iq and d-q method of first proposed require the phase-locked loop and low-pass filter. The paper make corresponding improvement on the basis of the method based on amplitude integration which only can detect fundamental current , propose a method which can detect the active and reactive current, and the method based on amplitude integration can detect fundamental current of single-phase circuit directly, and simulation. The simulation results show that the method can detect the harmonic and reactive current accurately and timely, and is suitable for various circumstances that three-phase power supply distortion and asymmetry and so on, and when only detecting the harmonic current, it does not require the phase-locked loop and low-pass filter, while detecting the harmonic and reactive current, increases the phase-locked loop; when the method based on amplitude integration is directly used to detect single-phase fundamental current, the phase-locked loop and low-pass filter are not required. The paper deduces the theory of the method and researches on simulation analysis.