Application and research development of Process Integration (PI) are discussed in process industry. Iron and steel industry is typical process industry and process integration model of iron and steel making process is constructed with energy consumption and contamination emission based on production process, production route and integrated enterprise. The factors of energy savings and emission reduction in iron and steel product route are analyzed. Results dedicated that systematic energy savings and emission reduction coming true by PI model, and measures and potential of improving energy efficiency and deducing pollution emission such as CO2 emission are put forward through optimizing the substance and energy structure by process integration.