The invention provides a CO detection based boiler combustion optimizing method and system as well as a database. The method comprises the following steps: obtaining first characteristic parameters, and obtaining boiler efficiency and a first characteristic curve according to the first characteristic parameters and a boiler efficiency calculating model; obtaining nitric oxide concentration in a boiler tail flue and a second characteristic curve; obtaining second characteristic parameters, obtaining comprehensive cost according to the second characteristic parameters, a comprehensive cost calculating model as well as a first characteristic curve and a second characteristic curve as well as a third characteristic curve; obtaining optimal carbon monoxide concentration according to the first characteristic curve, the second characteristic curve and the third characteristic curve, and storing the optimal carbon monoxide concentration into an optimized data base; and obtaining real-time carbon monoxide concentration, and regulating real-time carbon monoxide concentration through head air pressure of an air feeder according to the optimal carbon monoxide concentration in the optimized database. The CO detection based boiler combustion optimizing method avoids the problem that combustion regulation is affected as flue air leakage greatly affects O2 amount measuring results.