The invention discloses a production method of a low-alloy medium plate. The preparation method comprises the steps of converter steelmaking, external refining, continuous casting, heating, rolling and quick cooling. Steel comprises the following components in percentage by mass: 0.15-0.17 percent of C, 0.20-0.40 percent of Si, 0.55-0.65 percent of Mn, not more than 0.020 percent of P, not more than 0.020 percent of S, 0.020-0.040 percent of Al, 0.014-0.016 percent of Nb and not more than 0.30 percent of CEV (Carbon Equivalent Value). (P+F) microstructural characteristics of the traditional Q345E steel plate are maintained; the content of Mn is reduced by 0.9 percent in the component design, and a valuable alloy Ni is not added, thus the cost per tonnage of steel alloy is lowered; the Nb microalloying is carried out by matching with a TMCP (Thermo-Mechanical Control Process), thus the requirement of the property of the steel plate is met, the impact toughness is increased by about 90J; the CEV of the steel plate is reduced to below 0.30 percent, thus the welding property of the steel plate is greatly improved; and due to the adoption of measures such as great reduction of the alloy, removal of a ladle furnace process route and Direct Hot Charge Rolling (DHCR) of a hot casting blank, the production cost of the steel plate is greatly lowered.