The light weight heat treated B-grade bulletproof steel was developed through composition design and optimization based on multiplex alloying,multiplex micro-alloying design ideas and complex phase struc-ture strengthening theory. The puzzle how to avoid the quenching deformation problem of super high strength thin sheet was solved through heat treatment in a die with a set of cooling system. Such B-grade bulletproof steel plate has fine tempered lath martensite structure. The shooting and certification test results showed that the shoot resistance of B-grade bulletproof steel plate can meet the protection demand of Protection specification for cash carrying vehicles (GA 164-2005). In comparison with B-grade bulletproof steel plate made by one of the companies in Sweden,the weight of the developed B-grade bulletproof steel plate can be decreased by 8%under the same shoot resistance condition. It will be meaningful for cash truck and anti-hijacking vehicle to rea-lize light weight,energy conservation and emission reduction.