Prediction of knocking occurrence was examined in order to quantify knocking phenomena and evaluate combustion systems in pre-chamber lean burn gas engine. By the temperature two region combustion model and thermodynamics diagnostics the temperature of end gas was calculated. Empirical relations of instantaneous temperature and pressure of end gas for induction time was conducted by experiment of single cylinder engine. The single cylinder engine has a bore of 165 mm, a stroke of 185 mm and pre-chamber system with compression ratio of 13.2. Prediction of knocking occurrence was examined by Livengood-Wu integral. It was found that the temperature two region model could express combustion of pre-chamber gas engine and could evaluate combustion systems in pre-chamber lean burn gas engine.