A WSN image watermarking algorithm based on multi-wavelet was proposed. When the instability of image transmission in wireless sensor networks was considered, the proposed algorithm can increase the capacity of the image watermark. In this paper, the wavelet transform coefficients were analyzed by the noise visibility function. And the bits were embedded into the coefficients which have more ability to the tolerance of the noise according to the designated threshold. We achieved the adaptive adjustment in the watermarking strength combined with the JND in the wavelet domain. The experimental results show that the improved watermarking algorithm was adapted to a grayscale image. It can improve the information capacity and the identification capability of the grayscale images greatly. In addition, the renovated algorithm was feasible in the high-capacity watermarking and the watermarking capacity was increased obviously. It provided methods and means for the high-capacity watermarking, and also provided a new way for the further research in the new watermarking technology.