Over 270 million people have been infected by the coronavirus disease 2019 (COVID-19) in the past two years, resulting in 5 million deaths. The virus primarily transmitted through droplets or aerosols produced by coughing, sneezing, and talking. A full-scale isolation ward in Wuhan Pulmonary Hospital is modeled in this work, and water droplet diffusion is simulated using the Computational Fluid Dynamics (CFD) approach. In an isolation ward, a local exhaust ventilation system is intended to avoid cross-infection. The existence of a local exhaust system increases turbulent movement, leading to a complete breakup of the droplet cluster and improved droplet dispersion inside the ward. When outlet negative pressure is 4.5 Pa, the number of moving droplets in the ward decreases by approximately 30% compared to the original ward. The local exhaust system could minimize the number of droplets evaporated in the ward; however, the formation of aerosols cannot be avoided. Furthermore, in six different scenarios there are 60.83%, 62.04%, 61.03%, 60.22%, 62.97% and 61.52% droplets produced by cough deposited on the surface of the patient. However, the local exhaust ventilation system has no apparent influence on the control of surface contamination. This study provides several suggestions for the optimization of ventilation in the wards, and scientific evidence to ensure the air quality of hospital isolation wards.