Thick steel plate with excellent tenacity for excellent-tenacity welding heat affected zone and manufacturing method thereof

The invention discloses a thick steel plate with excellent tenacity for an excellent-tenacity welding heat affected zone and a manufacturing method thereof. The method comprises the following steps: 1) smelting, refining and continuously casting, wherein the thick steel plate comprises the following components by mass percent: 0.05-0.09% of C, 0.10-0.30% of Si, 1.2-1.6% of Mn, no more than 0.02% of P, 0.001-0.006% of S, 0.20-0.40% of Ni, 0.15-0.3% of Cu, 0.005-0.03% of Ti, 0.003-0.1% of Al, 0.0005-0.005% of Ca, no more than 0.02% of REM, no more than 0.02% of Zr, 0.0002-0.005% of B, 0.001-0.006% of N and the balance of Fe and inevitable impurities, wherein Ti/N is smaller than or equal to 6 and greater than or equal to 1; 2) rolling; 3) cooling. By adopting the manufacturing method, occluded foreign inclusions in fine dispersed distribution can be formed. By controlling the surface density of a micron occluded foreign substance of which the diameter is greater than or equal to 1 micron, the Ca/Al ratio and the length-width ratio of the occluded foreign inclusions, the surface density, the Ca/Al ratio and the length-width ratio of micron inclusions of which the diameter is greater than or equal to 1 micron, the surface density of a submicron occluded foreign substance of which the diameter is smaller than 1 micron, the tensile strength of base metal is greater than or equal to 510MPa, the welding line energy is 200-400 kJ/cm, and the welding heat affected zone has good impact toughness.