Understanding the deposition mechanisms of pharmaceutical aerosol in the mouth-throat (MT) is crucial to developing an in vitro method which aims to better predict in vivo lung deposition. This paper investigated the effect of geometrical variation, particle size and airflow rate on the fine particle deposition in the US pharmacopeia throat (USP), idealized mouth-throat (IMT) and realistic mouth-throat (RMT) models. The flow-field equations were solved with the SST model by computational fluid dynamics (CFD) and monodispersed particles in the size range of 1-30 mu m were tracked with discrete phase method (DPM). The results indicated that the deposition fraction and spatial distribution were highly sensitive to the geometrical variation and respiratory conditions such as the inhalation airflow rate and particle size. Moreover, the effect of geometrical variation on the particle escape pattern was more dominant. Comparing to the IMT model, more uniformly distribution of escape particles was observed at the outlet of RMT. While the total deposition fractions in IMT and RMT were similar, the spatial distributions of deposited particles were significantly different. In the RMT model, fewer particles were deposited in mouth and trachea, but the depositions in the pharyngeal and laryngeal regions were more uniform. These conclusions could help study the in vitro-in vivo correlation of dry powder inhaler systems. (C) 2018 Elsevier B.V. All rights reserved.