The Tarim basin located in the western northwest China is the largest inland basin in the world and the core component of the arid region of the Central Asia. In recent years, the frequency of heavy rain and extreme precipitation events in the Tarim basin has increased substantially. It is imperative to enhance the understanding of the triggering and development mechanisms of heavy rain in this region. This study analyzes the atmospheric instability and triggering mechanisms of a short-duration local heavy rainstorm event in the Tarim basin based on the moist potential vorticity (MPV) criterion. The results show that convective instability positively contributes to precipitation generation, while conditional symmetric instability assumes a pivotal role in its intensification. The cold air from northern short-wave trough with moist air from southern short-wave trough converge with the warm and dry air in the low layer of the Tarim basin, triggering the rapid release of convective available potential energy and the initiation of precipitation. Subsequently, the release of condensation latent heat and moist baroclinicity amplify the conditional symmetric instability in the lower atmosphere. The westerly wind over the mountains and the easterly wind in lower layers of the basin form intense vertical shear of horizontal wind. This vertical shear triggers the release of conditional symmetric instability energy, which stimulates further development of vertical motion and causes a sudden increase of precipitation. Although there are no obvious convective cloud systems, the rapid and intensive release of instability energy results in strong negative temperature variation, humidification, and wind shear, and their centers are overlapped. Such synoptic configurations are responsible for the local heavy rainstorm. The findings of this study contribute to a better understanding on the causes of short-duration local rainstorms in arid areas and offer valuable insights for improving rainstorms predictability in the region.