Abstract: Sensor design and signal de-noising analysis is the key issues of the alternative current field measurement system that must be addressed. Through exerting the coil core, reducing the structure size of the sensor, using differential series structure for the picking-up signal part of the sensor, and adopting the multi-stage amplification, filtering and demodulation circuits, the small defect signals were enhanced. At the same time, the appropriate wavelet mode was selected to denoise the signal acquisition, and the relationship was analyzed about the disturbance magnetic field and the caused defect. Testing results showed that, the stronger peak-peak value and low noise signal could be obtained by the optimized differential series structure sensor, so it was helpful to pick-up the weak disturbance magnetic field signal; the use of wavelet denoising method could help to reflect the signal quantitative characteristics more clearly.