Passive coherent beam combination of high power fiber laser arrays is researched theoretically and experimentally. Some typical technologies of passive coherent beam combination of fiber laser arrays are introduced, and their power scaling is analyzed. The principle of passive coherent beam combination based on ring cavity is analyzed. The coherent output spectrum characteristics and array size scalability of the passively coherently phased fiber laser arrays are explored. High power passive phase locking of 4-channel and 8-channel fiber amplifier arrays with ring cavity are experimentally demonstrated, and the maximum coherent output powers are up to 1062 and 1090 W, respectively.