The invention discloses a semi-high speed steel break-down (BD) roller and a manufacturing method thereof, particularly relates to a roller applied to a profile steel rail beam BD rolling mill and belongs to the technical field of roller manufacturing. The whole roller is made of semi-high speed steel. The alloy components of the roller comprise, by weight, 0.3-1.5% of C, 0.2-1.4% of Si, 0.2-1.0% of Mn, 1.5-5.0% of Cr, 0-1.0% of Ni, 0.5-2% of Mo, 0.5-1.5% of W, 0-1.5% of V, and the balance Fe and inevitable impurities. The manufacturing method comprises the steps of raw material smelting, integral casting, heat preservation and demolding, heat pretreatment and heat treatment. According to the heat treatment, the high-temperature quenching technique and the high-temperature tempering technique are adopted. According to the structure of the roller, 3% or less of granular carbides are distributed on tempered sorbite, the macro-hardness of the roller is controlled to be HSD50-70, the abrasion resistance is high, the tensile strength is equal to or higher than 800 MPa, the crack extension resistance is high, and the roller is good in roller surface quality under the off-machine condition and small in abrasion under the on-machine condition; and the requirements of rail beam rolling can be well met, and especially the requirements for high strength, high abrasion resistance, high impact resistance and high hot cracking resistance of the roller in the rail beam rolling process can be well met.