The invention discloses a method for assisting in dephosphorization in an earlier stage of semisteel steelmaking by utilizing converter dust-removing ash. The converter dust-removing ash and lime areadded into a steel ladle in the steel tapping process of vanadium recovery semisteel, then semisteel contained the dust-removing ash is added into a converter for steelmaking. According to the method,the dephosphorization rate in the earlier stage of semisteel steelmaking reaches more than 80% by adding proper cold charges and controlling of the lance position and oxygen flow in accordance with the phosphorus content and the temperature of the semisteel; the iron content of the dust-removing ash is high, specifically, TFe is 55-70%, and FeO is 20-35%, the dephosphorization condition of the semisteel can be met, materials such as machine burning ore and oxidized scale can be greatly reduced or completely replaced, not only is secondary utilization of resources achieved, but also the metallic yield is effectively improved, and production cost is reduced accordingly; and meanwhile, the dephosphorization efficiency of semisteel steelmaking is improved, and slagless steelmaking, shorteningof the smelting period and improving of the production capacity can be achieved by the converter; and meanwhile, the problem of resource reusing of the converter dust-removing ash is solved.