A small scale of intraplatform biological reef rock was discovered in the Middle Permian Maokou Member-3 at Well Yue-005-H1 in the east of Sichuan Basin. Based on observation of drilled cores from this well, it is shown that the reef rock is mainly composed of algal framework reef limestone. Reef-building organisms mostly are phylloid algal and seldom bryozoan with a few epiphyllous organism and a plenty of marl and biodetritus are deposited among the algae sheets. Two complete sedimentary cycles, in which any a single cycle is about 1.5m thick, can be recognized in vertical in reef rock and every cycle can include four development phases. Some subfacies, such as reef base, reef core and reef cap (flat) facies, can be classified in reefs. It is inferred that this kind of algal reef limestone that formed on the shallow water carbonate faulted-uplift is likely to be relative with middle Permian Maokou karst weathering-crust reservoirs.