The Changxing Formation in the northeastern Sichuan Basin is in a marine environment, and can be divided into a carbonate platform sedimentary system and a basin sedimentary system based on sedimentary characteristics. The carbonate platform sedimentary system is further divided into such facies as restricted platform, open platform, platform margin reef and ramp. In this paper we discuss spatial distribution of the sedimentary facies belts, and argues that the Kaijiang-Liangping ocean trough does not exist. The Changxing Formation is the result of a deep-water environment relative to platform, and it is located on a carbonate ramp, instead of an ocean trough. We point out that platform margin shoals and organic reefs are the best favorable facies belts of reservoirs, and reef dolomite and grain dolomite are the favorable microfacies of reservoirs. Organic reefs in the study region form a patch reef group on the carbonate platform margin ramp and they are interruptedly distributed along the platform margin.