A 250 mm thick low-carbon high-toughness low-alloy S355NL steel plate, comprising the following chemical components in percentage by weight: C: 0.07-0.14%, Si: 0.15-0.25%, Mn: 1.40-1.60%, P≤0.006%, S≤0.001%, Al: 0.02-0.06%, Nb: 0.02-0.05%, V: 0.02-0.05%, and Ni: 0.30-0.50%, with the balance being Fe and inevitable impurity elements. The manufacturing process comprises: KR pretreatment → converter smelting → LF refining → RH refining → slab continuous casting → slab slow cooling → slab heating → steel plate rolling → steel plate slow cooling → flaw detection → normalization → finishing → inspection → warehousing. The steel plate of the present application is manufactured using a 450 mm continuous casting billet, where the heat treatment process is simple, the production costs are low, mass production can be achieved, and excellent low-temperature impact toughness and good comprehensive mechanical performance are given after normalization.