This paper undertakes the experimental and numerical investigations on the degraded mechanical behaviors of high performance steel (HPS) beams subjected to local corrosion within the shear-span due to ocean aggressive environments. Six Q460D steel specimens were fabricated and divided into two groups, i.e., two reference beams (RB) and four beams with local corrosion within the shear-span (SCB). Accelerated corrosion was employed to obtain the target corrosion level. The geometric characteristics of the corroded beams were analyzed and characterized by using 3D scanning. Mechanical behaviors, including load-deflection response, strain development, and failure modes, were investigated in detail. In addition, the impact of corrosion level and length on mechanical properties was numerically analyzed and compared with the Q235 beams. Experimental results show that obvious degradation of flexural strength and rotational stiffness appears when the corrosion level is higher than the critical corrosion value (about 10%). Failure behavior presents from progressively weakening buckling wavelengths and decreasing vertical deflection to the gradually forming diagonal tension stress band on the web and developing plastic hinges on flanges. Sharply degraded strength and stiffness of the HPS beams are found when severe corrosion (about 70%) occurs within the shear span near the support. The stiffness degradation of the HPS beam is similar to that of the Q235, but the ductility and critical position are different.