To Solving the high false problem of SVD (singular value decomposition) based algorithm, a DDPCA (doubledecomposition principal component analysis) based improved image watermarking algorithm with reliability is proposed in this paper. The principal component of the watermark is extracted with SVD and embedded into the singular values of the host image. Then the second SVD is used creatively. After ISVD， the watermarked image is obtained. Experimental results show that the algorithm proposed is well imperceptible and robust to noising, compression, blurring and geometric attacks.