Steganography is an important branch of information hiding techniques.Different from other information hiding techniques,the embedder has the freedom to choose a cover images which results in the improvement of the undetectability of image steganography.This paper exp lores the relation between cover image characteristics (variance,complexity,entropy,histogram and function of histogram ) and steganography performance (relative entropy and change of histogram) to find whether image characteristics affect or decide the steganography performance.The results provide basis for cover selection of image steganogra phy.Experiments show that the selection of the proper cover image is a more effe ctive way to improve the undetectbility of steganographic systems.