At the Permian Baliklik Formation in the northwest margin of the Tarim basin, there developed massively thick reef limestone that bears oil and gas exploration significance. This paper makes macro and micro examinations of the reefs which cropped out at Kizilbulak Nangou in the northwest margin of the Tarim basin. This set of reefs had bioclastic shoals as reef bases. The lower zone of the reef core is mainly composed of microbialite of various types formed by Cyanobacteria, with thrombolite and brokenup microclots as its most dominant structural components, followed by stromatolites. At this time, the hydraulic energy is low. In the upper zone of the reef core locally developed phylloid algal reefs, with a large quantity of marine benthic fauna among them. At this time, the reef body began to expose itself above the wave base, with a large number of brecciated limestone developed, and it was subjected to the transformation of atmospheric freshwater karstification. In addition to the platform margin zone, the synchronous restricted platform in the Keping area in the northwest Tarim basin also developed smallscale intraplatform reefshoal complexes, with microbial rock characteristics, indicating that the environmental conditions in the region during this period were generally favorable for reef building. The set of reefshoal complexes in the Baliklik Formation formed in the Late Atherian period of the Cisuralian to the Sa kmarian age, contemporary with the early stage of large igneous provinces of Cisuralian Tarim basin. Therefore, it is speculated that the forming of this set of reefshoal complexes was related to the “eutrophication” of the sea water in the residual basin of the south Tianshan ocean; the “eutrophication” had been caused by the volcanic ash spurted out by volcanic activities at that time. As a result of the outbreak of algae, the δ13C value of the reefshoal complexes in the Baliklik Formation shows a significant positive shift compared with that of the carbonate rocks in the Kangkelin Formation. However, the reefshoal complexes of the Baliklik Formation was much transformed by cementation and other constructive types of diagenesis, unfavorable to the forming of reservoirs. In other words, the reefshoal complexes of the Baliklik Formation in the region,despite their desirable facies belts, possess poor reservoir permeability; high permeability layers only developed where structural fractures occurred. Therefore, it can be theorized that reefshoal reservoirs of the Cisuralian Baliklik Formation in the northwest margin of the Tarim basin are, generally speaking, not controlled by facies, and that fractured reservoirs were dominant. Thereupon, exploration of Permian reefshoal oil and gas reservoirs in the northwest margin of the Tarim basin should focus on the structural fractured members. In brief, this study is an attempt to provide some scientific basis for the prediction of highquality reservoirs in the Baliklik Formation reefs of the Tarim basin, and to promote further research into Permian microbial rocks in China and throughout the world.