There were lots problems in the 4 500t/d cement clinker production line such as high coal consumption, large resistance of the pre-calcining system, low capacity, poor system heat exchange, serious coating, low cooler efficiency, and large consumption of denitrification ammonia. Combined with production practice and process design research, the expansion of calciner volume, the expansion of the ventilation area at the inlet of the cyclone, the optimization of riser duct of the kiln inlet chamber, the resistance reduction of the preheater system, the replacement of the high-efficiency splash box and the air lock valve, and the use of low-nitrogen staged combustion technology, the fourth-generation high-efficiency grate cooler are adopted. The negative pressure at the outlet of the C1 cyclone is reduced to 5 000Pa, the NOX concentration is controlled at about 450mg/m3 before the treatment of the SNCR system, and the clinker temperature out of the grate cooler is 65℃+ ambient temperature, the physical coal consumption is reduced to 136.5kg/t.cl, the annual comprehensive economic benefit can reach to 33 million yuan, and the effect of energy-saving transformation is remarkable.