Based on profile measuring，applied the microscopy and SEM technology，the micro texture characteristics of chert in Sinian Dengying Formation in eastern Chongqing has been studied. And features of oxygen isotope are also discussed in this paper. The formation mechanism of chert has been analyzed at last. Four understands have been gotten in this paper，whose are: (1) Chert of Dengying Formation comprise of cryptocrystalline quartz，chalcedony，microcrystalline quartz and megacryst quartz fabric elements，and cryptocrystalline, microcrystalline and poikilotopic fabric types have been found in the chert. Survival dolomite is also found in the chert，and boiling pinholes which respond to hydrothermal fluid are very abundant in chert. (2) Value of δ30Si in chert ranges from-0.6‰ to 0.8‰，which belongs to the range of hydrothermal chert. The value of δ18O in chert ranges from 15‰ to 23.5‰. The hydrothermal temperature，which calculated by the oxygen isotope in chert mainly ranges from 70 to 110℃. (3) Geochemical features of main elements and REEs reveals that chert origins in hydrothermal fluids，and affected by the structural geographic location and sea water. (4) The formation mechanism of chert is controlled by multi factors，sea water，hydrothermal fluid，deposition and diagenesis. The formation time of chert ranges from late Sinian Dengying stage to early Cambrian Niutitang stage.