Abstract: One kind of digital image hiding algorithm based on DCT transform is proposed here.The steps are as follows,the carrier image matrix is fristly DCT transformed after divided into blocks,each block of the transformed matrix used to store details of the image is to store the DCT matrix elements of the the encrypted cecret image,the final hidden image is shaped after an inverse DCT transform block.The final hidden image and the original carrier image is almost the same from the naked eye.The method above is used to safely hide a secret image.The effectiveness of the hiding algorithm,hidden properties,the recovery effect of the hidden image when extracted are all deeply analysised from several aspects as follows,the numerical parameter index analysis,the size of secret key space,secret key sensitivity and the ability to resist breakage attack.