In recent years, basalt-fiber-reinforced polymers (BFRPs) have been widely used in the field of corrosive aging resistance. In this paper, BFRPs are made into composite laminates, and the flexural properties of BFRPs modified with different types of silane coupling agents, KH550 (aminopropyl-triethoxysilane), KH560 (glycidyletheroxypropyl-trimethoxysilane), and A171 (vinyl-trimethoxysilane), immersed at 20 °C, 40 °C, and 60 °C in a 3.5% NaCl concentration artificial seawater, a 10% NaCl high-concentration artificial seawater, 10% H₂SO₄, or 10% NaOH are investigated. The results show that the flexural strength decreased with increasing exposure time in corrosive aging environments at different temperatures. The temperature greatly influences flexural strength, and the flexural strength decreases rapidly in high-temperature acidic and alkaline environments. In addition, we found that the flexural retention in the seawater environment did not change much compared to that in the water environment, indicating that BFRPs have relatively good resistance to seawater corrosion. The silane coupling agent modification enhances flexural strength and flexural strength retention by enhancing the interfacial bonding property of the BFRPs. Considering the experimental results, the three silane coupling agents modified the corrosive aging performance of the composites in the order of KH550 > KH560 > A171. This will provide theoretical support for the application of silane-coupling-agent-modified BFRPs in corrosive aging environments.