The work is devoted to the calculation of gas flow and modeling of droplet sedimentation of medicinal aerosols in human lungs. To solve this problem, a previously constructed three-dimensional model of a human bronchial tree was used. For calculation of gas flow in lungs and aerosol deposition the method of step-by-step calculation of the flow in bronchial tree was used. It allowed to calculate the air flow and aerosol droplets deposition in all bronchial branches up to alveolus. Human breathing was calculated using COVID-19 thermal helium-oxygen mixture treatment method. Breathing with a thermal helium-oxygen mixture requires less effort from the patient than breathing with air. Three-dimensional numerical calculations of air flow and aerosol droplets in human lungs have been performed. The characteristics of a serial medical nebulizer were used to calculate the deposition of aerosol droplets. It is shown that the number of past droplets depends (except for flow, droplet size) on the duration of breath. The nebulizer under consideration does not provide delivery of medicines to the lung alveolus.