Through the 1∶50, 000 regional geological survey and cross- sectional study, a large set of rhyolite tuffaceous slate interlayers was discovered in the Heishan Formation in the Dongchuan area of Yunnan Province in the western margin of the Yangtze River. Results: The LA- ICP- MS zircon U- Pb age- weighted average of 1522±15 Ma was obtained from the rhyolite tuffaceous slate. At the same time, a microbial sedimentary structure (MISS) was found in the argillaceous slate of the Heishan Formation in the Mesoproterozoic. Through the electron probe, XRF analysis and energy spectrum analysis of the MISS and surrounding rocks, it was found that the main components of the MISS are: P, S, Fe, Cr are obviously the characteristics of compounds formed in the process of microbial deposition. while the surrounding rocks are mainly Al, Si, K, Mg, Ti, which are normal clay minerals, and there is a big difference between the two. The MISS discovered this time is the oldest MISS known to be discovered in the southwestern margin of the Yangtze River. Conclusions: The appearance of MISS in the Heishan Formation indicates that the microbial community flourished in the Mesoproterozoic period, reflecting that the depositional environment at that time was the coastal shallow water supratidal zone. The microbes at the sag participated in the formation of such an irregular striped wrinkle structure, which provided important reference materials for the regional comparison of Mesoproterozoic stratigraphic microbes and paleoenvironmental research, it is of great significance to restore the bio- sedimentation and environmental evolution of the Kang- Dian rift basin.