The thermodynamics, dynamics in the process reducing molybdenum oxide(MoO3)to molybdenum by the elements in molten iron such as silicon,carbon etc.,and the quality of molten iron was analyzed.lt was pointed out that when molybdenum content was lessthan 1%,the molybdenum absorption ratereached 95%or more by adopting the method of adding molybdenum oxide into ladle.Using molybdenum oxide as substitute of ferro-molybdenum resulted both in good quality of molten iron and in reducing cost of iron castings.