High concentrations of airborne particulate matter in factories can cause serious health problems for workers. One significant reason for these high concentrations is the poor performance of the ventilation systems in workplaces. This investigation developed a strategy that combines computational fluid dynamics (CFD) simulations and on-site measurements to study and improve the ventilation performance in factories. The CFD simulations were able to predict the flow field and particle distributions in factories with complex layouts. The corresponding on-site measurements were performed to provide boundary conditions for the CFD simulations and to obtain key data about airflow and air quality for validating the simulations. This study used the strategy to improve ventilation performance in an automotive parts factory. Three ventilation systems were studied: a roof exhaust system, combined roof exhaust and air recirculation systems, and combined roof exhaust and displacement ventilation systems. This study found that the combined roof exhaust and displacement ventilation systems provided acceptable indoor air quality and thermal comfort levels in the factory.