The research on crack detection under coating of current components， the adaptive second-generation wavelet transform is applied to the array eddy current detection. The array eddy current testing can suppress the lift off effect and is not affected by the direction of defects. The adaptive second generation wavelet can effectively match the signal features， eliminate the influence of noise and improve the signal quality. The experimental results show that the array eddy current testing method based on adaptive second generation wavelet transform can effectively identify the cracks under the coating of the flow passage parts of hydropower station， with high detection accuracy and strong adaptability， and has good engineering application value.