The encryption of images is quite different from that of the texts due to the bulk data capacity and high redundancy of images. Traditional methods are difficult to handle the image encryption because of their small space of pseudo random sequence. At present, the chaotic maps have been widely used in image encryption for their extreme sensitivity to tiny changes of initial conditions. The chaos based algorithms have suggested a new and efficient way to deal with the problem of fast and highly secure image encryption. In this paper, we analyze the chaotic features of traditional trigonometric function and propose a new chaotic image encryption algorithm. The algorithm uses a chaotic map base on trigonometric function as a mask to confuse the plain-image and employs several different types of operations to shuffle the image pixels according to the outcome of another chaotic map. Thereby it significantly increases the resistance to statistical and differential attacks. The results of experiment, statistical analysis, correlation coefficient analysis and key sensitivity tests show that the algorithm is of great security and practicability.