In the production management as well as in the information technology that supports it, automatically transforming engineering BOM(EBOM) into manufacturing BOM(MBOM) is the key problem of integrating product design system with production planning system. A method of quickly, accurately and automatically transforming EBOM into MBOM based on the bill of process(BOP) is developed. The strict formal definitions of EBOM, MBOM, BOP and the transformation rules of product structures, lead-times and process routines are presented. Based on those, an algorithm of automatically transforming EBOM into MBOM is proposed. Finally, a case from practice of this transformation method in an electric machinery manufacturing enterprise indicates its effectiveness and feasibility.