In-situ resource-based construction techniques can greatly reduce the cost of lunar surface base construction and guarantee high-quality operation and maintenance. How to make full use of in-situ resources to prepare high-performance building structural materials has become a hot research topic. In this study, geopolymers were prepared using lunar regolith simulant and reinforced with basalt fibers to enhance the mechanical properties of the materials.The effects of basalt fiber content on the failure modes and mechanical properties of lunar regolith simulant geopolymers activated by strong and weak alkali solutions were investigated. The results showed that the incorporation of basalt fibers changed the failure modes of lunar regolith simulant geopolymers and increased their deformation capacity. Under the condition of strong alkali solution activation, the optimal content of basalt fiber was 0.2%; while under weak alkali activation, the optimal content was 0.1%. The compressive and flexural strengths of the lunar regolith simulant geopolymers tended to increase and then decrease with the increase of fiber content. Compared with the strong alkali environment, the basalt fiber content had a more significant effect on the lunar regolith simulant geopolymers in the weak alkali environment.