Low-cost, high-performance ultra-high-strength steel for construction machinery and its manufacturing method, its composition weight percentage is: C: 0.18% to 0.22%, Si: ≤0.10%, Mn: 1.30% to 1.60%, P: ≤0.013%, S: ≤0.0030%, Cr: 0.30%~0.60%, Mo: 0.10%~0.30%, B: 0.0010%~0.0020%, Ti: 0.008%~0.018%, Nb: 0.010%~0.030%, Al: 0.030% ~0.070%, N: ≤0.0050%, O≤0.0030%, Mg: 0.001%~0.004%, the rest is iron and unavoidable inclusions. The invention adopts the combination of controlled rolling + online DQST, on the basis of adding a small amount of precious Mo alloy, while obtaining ultra-high strength, the low-temperature toughness, weldability and fatigue impact load resistance of the steel plate are also excellent, and successfully solves the problem of ultra-high strength. The contradiction between the strength, low temperature plasticity and toughness, delayed crack resistance and weldability of high-strength steel plate and the problem of overquenching of the surface (sub) surface of the steel plate.