The invention provides Cu-containing nanophase strengthened easy-to-weld steel and a preparation method. The Cu-containing nanophase strengthened easy-to-weld steel comprises the following components by weight percent: less than 0.05% of C, 0.1-0.3% of Si, 0.5-1.5% of Mn, less than 0.002% of S, less than 0.004% of P, 1.5-2.5% of Cu, 4-8% of Ni, 0.3-0.8% of Al, 0.2-1% of Mo, less than 1% of Cr, 001-0.04% of Nb, 0.01-0.05% of Ti, 0.01-0.08% of V, and the balance of Fe and inevitable impurity elements. The preparation method comprises the following steps: performing induction smelting and casting under argon protection; heating cast ingots at 1,100-1,200 DEG C for 1-3 h, directly performing hot rolling at the initial temperature of 1,050-1,150 DEG C and the final temperature of 950 DEG C, and performing super-speed high-pressure water cooling after final rolling, wherein the hot rolling deformation is 50-90%; and selectively conducting solution and aging heat treatment on a rolled steel plate to obtain high-strength high-toughness easy-to-weld steel. The alloy steel is high in strength, good in plasticity, excellent in low-temperature impact toughness and easy to weld. Besides, the machining process is high in controllability, the cost is low and the operation is simple.