The objective of the work presented in this paper is to provide an overall CFD evaluation and optimization study of cabin climate control of air-conditioned (AC) city buses. Providing passengers with a comfortable experience is one of the focal point of any bus manufacturer. However, detailed evaluation through testing alone is difficult and not possible during vehicle development. With increasing travel needs and continuous focus on improving passenger experience, CFD supplemented by testing plays an important role in assessing the cabin comfort. The focus of the study is to evaluate the effect of size, shape and number of free-flow and overhead vents on flow distribution inside the cabin.Numerical simulations were carried out using a commercially available CFD code, Fluent®. Realizable k - ε RANS turbulence model was used to model turbulence. Airflow results from numerical simulation were compared with the testing results to evaluate the reliability. Qualitative parameters such as mean Age of Air (AOA), Broadband Noise model, and Human Thermal Comfort Module (PMV/PPD) were used to gain deeper insight into the problem. Results of this study provide a valuable reference for designing a ventilation system of vehicles of mass transportation, to achieve balance between passenger comfort and energy conservation for air-conditioning unit.