This paper describes the development process and test results of the lean burn engine. LML (Lean Misfire Limit) extension and NOx emission reduction was realized in combination with the following factors. (1) Installing several types of SCV (Swirl Control Valve) with different section shapes and dividing wall in the intake port intensified the flow field inside combustion chamber, so optimized mixture formation and combustion improvement were obtained. (2) By precisely controlling injection timing, changing injection rate, thus obtaining locally stratified charging, LML was extended. (3) By intensifying ignition system, better combustion characteristics were achieved. (4) NOx emission was reduced by extending LML and adopting lean NOx catalyst (Cu-ZSM-5). By combining above factors, we extended LML to A/F 23. Therefore NOx emission was reduced 60.6%, fuel economy was improved 10.6% in engine dyno test. BY ECU mapping test, we fixed lean operating zone.