Through a comparative analysis of multiple schemes, a reusable LO/LH propulsion-based single-stage lunar landing and ascent spacecraft scheme with vertical landing in horizontal attitude was proposed. For the problems of large fuel consumption and low control accuracy in braking phase, a convex-optimization-based guidance method was proposed. The convex optimization was then modeled and simulated, and the influence factors were analyzed. The results show that the scheme is easy to implement and reliable, capable of matching new-generation human launch vehicles, and the method possesses good mission applicability, enabling fuel cost optimization with various constraints including landing attitude and position accuracy. The proposed reusable single-stage lunar landing and ascent spacecraft scheme can be applied to lunar and cis-lunar reusable transportation missions, and provides a possible integrated transportation vehicle for both Earth orbit and lunar surface, holding a high cost-effectiveness ratio. The proposed scheme also provides a good solution for future transportation system for large-scale cis-lunar exploration and exploitation.