Abstract: With the decrease in the size of cubic silver halide crystallites, the resolution of silver halide photographic emulsion increases, meanwhile, its sensitivity decreases rapidly. The structure of silver halide microcystal grains has great influence on the sensitivity. In this paper, the design principle of multi-structure silver bromo-iodide is investigated. Silver halide photographic emulsion with multi-structure grains is precipitated by auto-controlled double jet machine. TEMand XRD analyses showthat iodide-rich layer is composed ofAgBr0.831I0.17, in which iodide is not distributed uniformly and mainly located near the corners of the cubic core grains. XPS analysis shows that the surface of multi-structure grains contains some iodide ions though no iodide has been added, suggestingthatthe iodide ions have the tendencyof diffusing outwards. In addition, the experimental phenomena are explained in theory.