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Objectives : Nitrogen removal processes are very important in terms of water conservation. Among them, the MLE process has been difficult to optimize because it has many variations and required experiences in operation. Methods : In this work, we quantitatively analyzed the nitrification of the MLE process using the STOAT simulation program. In particular, we attempted to improve nitrification rate even at lower water temperatures. Results and Discussion : As a result, more than 93% ammonia was nitrificated when the water temperature was above 20℃, and a lower reduction rate of ammonia was observed when the temperature was below 15℃. Simulations applying three process variables (MLSS, DO concentration, and RAS) were carried out once or several times to increase nitrogen removal efficiency at 10℃, and the most efficient variable was ‘RAS increase’(55% reduction of ammonia). Conclusions : For more efficient nitrification rate, simultaneous increases in RAS and DO were required. In this case, the ammonia concentration in the effluent dropped by 61.4% and it was desirable to increase the MLSS return volume for T-N concentration reduction.