Prediction of bacteria-carrying particle dispersion and distribution released from personnel in an operating room has been simulated by means of computational fluid dynamics technique. This investigation is focused on the performance and influence of a local ultra-clean laminar ventilation system on the airflow field and the particle distribution in an operating room. A RNG k-ε turbulence model was used to map the airflow field. Particle movement was simulated using Lagrangian DRW particle tracking method. It is shown that, MLAF can play a key role in the microorganism transmission over the instrument and operating tables. Counts of particles reveal obvious declining trends as the MLAF airflow speed increased.