Dark gray thin-bedded limestones intercalated with very thin-bedded grayish black shales as well as the depositions of contour currents are very developed in the lower part of Kelimoli Formation in Middle Ordovician of Zhuozishan area of western Ordos basin. And the Shixiagu section is an ideal one for studying sedimentary processes of contour currents because of its perfect preservation of thin-bedded limestones with slight lenticular shapes which have little post-depositional effects. Based on the detail fieldwork, we further ascertain deep-water slope depositional environments and contour current depositions from sedimentary structures, characteristic and association of sedimentary rocks. Apart from these, this article focus on the depositional mechanisms and hydrodynamics of thin-bedded limestone from its characteristics of fillings and shapes. The results showing that: �� the differential textures and slight cycles are common in single thin-bedded limestone and between them in the section respectively; �� limestones are mainly developed grain-size (crystal grain of calcites) related sedimentary structures which include bigradational grading, banded structure and parallel- uniform-parallel succession; �� multi limestone beds could be formed lenticular shape with symmetric pinch in single beds and the hole lens are pinching out in both shale and high topography; �� Thinning-upward packages and its amalgamated beds are developed in the study section; �� comparatively thin limestone bed (thin bed) commonly consists of micrites with continuous small-scale lenses and incomplete uniform-parallel succession; �� comparatively thick limestone bed (thinly medium bed) commonly consists of microcrystalline limestone with long lenses and complete parallel-uniform-parallel succession. Using the previous research, we propose for the depositional environment of thin-bedded limestones in the lower part of Kelimoli Formation is deep-water contour currents channel, and their depositional mechanisms can be divided into 3 stages which include clear water deposition of calcites before contour currents action, re-deposition during contour currents action and the mixing water deposition of mud.