Steel output per unit GDP is an important index for controlling steel output,  for energy-saving, materials-decreasing and wastes-reducing of steel industry. This paper first gave the definition of steel output per unit GDP, introduced the concept and calculating formula of "in-use steel", Then two times of transformation for the definition formula of steel output per unit GDP were undertaken to obtain the new definition formulas with analytic function. Steel output and energy consumption,  materials consumption & wastes emission of steel industry were analyzed by using the new definition formulas of steel output per unit GDP, calculating formulas of steel output,  energy consumption,  materials consumption & wastes emission. Finally parameters related to steel industry were categorized and overall view for comprehensive promoting energy-saving, materials-decreasing and wastes-reducing of steel industry were put forward.