Abstract: To address the difficulties of complicated formwork, of restricted construction conditions and, of the poor control of forming quality in the strengthening of damaged reinforced concrete (RC) structures, eight pre-damaged RC beams were strengthened at the soffit using sprayed ultra-high-performance concrete (UHPC) and cast-in-place UHPC. Four-point bending tests and finite element analysis were conducted to systematically investigate the failure mode, the deflection behavior and, the load-carrying capacity of RC beams strengthened with different UHPC layer treatments. The test results showed that the UHPC strengthening layer bonded well to the original beam soffit and exhibited clear composite action with the existing beam. Both strengthening methods significantly increased the cracking load and the ultimate load of the RC beams, with increases of about 28%-80% in cracking load and 34%-42% in ultimate load. Compared with cast-in-place UHPC, the beams strengthened with sprayed UHPC showed more fully developed and more uniformly distributed cracks, while their ultimate load remained comparable. The thickness of the sprayed layer significantly affected the strengthening performance. A spray thickness of 50 mm provided improved load capacity with better economy. Considering the effective tensile contribution of sprayed UHPC, a flexural capacity model for RC beams strengthened with sprayed UHPC was established. The relative error between the calculated and test values was within 10%, indicating a good agreement. Sprayed UHPC effectively improved the flexural performance of damaged RC beams and showed a good potential for engineering application. A spray thickness of 50 mm is recommended in practice, and the reinforcement mesh should be arranged according to the structural demand and to construction conditions to achieve better strengthening efficiency and economy.