Unsteady uvula motions and the resultant pressure oscillations within the pharyngeal airway are critical for the pathology of snoring and sleeping apnea. In this paper, an immersed-boundary-method based direct numerical simulation flow solver was adopted to simulate the unsteady flows in an anatomically accurate pharynx model reconstructed from human magnetic resonance images (MRI) with prescribed uvula oscillation and airway obstruction. In order to study the influence of uvula length on the aerodynamics of pharyngeal airflow, simulations were conducted using various uvula models with scaled uvula lengths at 25%, 50%, 75%, and 100% of the original length, respectively. Analyses of vortex dynamics, pressure oscillations, and the aerodynamic force of uvula were conducted. It was found the length of uvula had significant impacts on vortex development as well as aerodynamic pressure/force. Shorter uvula induced weaker pressure oscillations and fewer vortices in the airway. Further fast Fourier transform analysis of pressures from different pressure probes showed higher-order harmonic waves other than the base frequency of uvula motion. This study is expected to bring understanding of snoring and sleep apnea and provide guidance for surgery.