This paper present a study about developing a defrost performance of the mini vehicle. Defrost performance of vehicle, specially de-ice performance is one of major contributed factor to safe driving on secure vision area view point. Major keys for secure vision area of a windshield are uniformity of airflow pattern at defrost duct outlet. Generally, a mini vehicle has small packaging area to place a HVAC(Heating, Ventilation and Air-Conditioning) module and ducts having symmetrical geometry. There are lots of restriction to develop HVAC module and ducts because of small space. Position and geometry of HVAC module and ducts have negative effect to have uniformity of airflow pattern at defrost duct outlet. For this reason, developing defrost performance in a mini vehicle is required lots of study. This study was performed by CFD CAE to optimize defrost duct design to secure uniformity of defrost duct outlet airflow pattern. Validation results between physical climate chamber test and CFD simulation result are also discussed. Results show well matched for a defrost performance development by CAE.