The invention discloses zirconium-reinforced low-activation martensitic steel and a preparation method thereof. The zirconium-reinforced low-activation martensitic steel comprises, by mass, 0.01%-0.02% of C, 0.01%-0.05% of Si, 0.3%-0.5% of Mn, 8.0%-9.0% of Cr, 1.0%-1.5% of W, 0.2%-0.3% of V, 0.01%-0.03% of Zr, 0.01%-0.02% of N, 0.01%-0.02% of O, and the balance Fe. During preparation, Fe, Cr and Ware melted in a vacuum induction furnace; then, C is added for deoxidization; then, Zr, Mn, Si, V and C are added in sequence, and after all alloys are melted down, casting is performed under nitrogen protection to obtain a cast ingot; the cast ingot is subjected to component uniformity adjustment and then machined into a rolling billet; and the rolling billet is rolled, slow cooling is performedafter rolling is completed, and then quenching and tempering are performed to obtain the zirconium-reinforced low-activation martensitic steel. According to the method, by adding zirconium instead ofTa for reinforcement, an oxide zirconium reinforcing phase and nano-scale zirconium carbide can be formed, and the use performance of the steel is improved.