Based on blocked image scrambling encryption, this study presents a new image encryption algorithm by introducing chaos theory. This algorithm firstly makes spatial scrambling based on image blocking in order to interrupt pixel position, then furthering this interruption through Arnold Mapping in the chaos and transforms pixel RGB color space through optimized Arnold Mapping. After this process, we get the final encrypted image through a series of iteration. This algorithm has a lot of advantages such as a large key space, high effectiveness and resisting common attack successfully, but it needs improvements on some aspects, such as the key sensitivity