Abstract: It is generally considered that the reservoir properties will be destroied once silicification occurs in carbonate reservoirs, leading to difficulty in the storage of oil and gas. However, some scholars have found that siliceous rocks originated from completely corroded carbonates can also develop dissolved pores, where oil and gas have also been discovered. There still lack systematic studies on the genesis of silica in the Lower Cretaceous lacustrine carbonate rocks of Campos Basin, relationship between silica and reservoir space, and evolution law of the reservoir space. After the silicification of carbonate rocks, it is difficult to grasp the changes in the evolution of reservoir porosity. Based on previous studies and the analyses of microscopic rock characteristics under microscope and geochemical characteristics, the paper investigates the petrologic features, reservoir space types, silica source and storage space evolution law of Lower Cretaceous silicified carbonate reservoirs in Campos Basin. The results suggest that dissolved siliceous rocks can act as reservoirs; silica in carbonates was formed due to metasomatism, and silica-rich hydrothermal fluid flowed into the carbonate formations through major faults, producing a cementation and metasomatism on the carbonate rocks; there were multi-stage hydrothermal fluid activities, including the dissolution of original carbonate rocks, cementation and metasomatism of silica, and dissolution of the siliceous rocks from completely corroded carbonate rocks. In general, the reservoir space evolution of the silicified carbonate rocks can be divided into five stages, including carbonate rocks with high porosity, siliceous carbonate rocks with medium porosity, carbonate siliceous rocks with low porosity, siliceous rocks with medium porosity, and siliceous rocks with high porosity. In addition, fractured-cavity type reservoirs with better physical properties can be found in siliceous rocks distributed along major faults.