The invention discloses a production method for a low-alloy medium-thick steel plate. The process route comprises the following stages in turn: converter steelmaking, external refining, continuous casting, heating, rolling, and accelerated cooling. Steel comprises the following components by weight percent: 0.15-0.17% of C, 0.20-0.40% of Si, 0.55-0.65% of Mn, less than or equal to 0.020% of P, less than or equal to 0.020% of S, 0.020-0.040% of Al, 0.014-0.016% of Nb, and less than or equal to 0.30% of CEV. The (P+F) micro-structural feature of the traditional Q345D steel plate is maintained by the steel plate; according to the design of the components of the steel plate, the Mn is reduced by 0.9%, no Ni is added and 0.015% of Nb is increased, so that the cost per ton of steel alloy is reduced; the Nb micro-alloying treatment is supplemented with TMCP (Thermo Mechanical Control Process) technology, so that the demand on the performance of the steel plate is met, the percentage elongation is increased by 2%-3% and the impact toughness is increased by about 90J; the CEV of the steel plate is reduced to below 0.30% and the welding property of the steel plate is greatly improved; and the measures, such as, the great reduction of the alloy, the eliminating of ladle furnace process route, the Direct Hot Charging Rolling (DHCR) of hot casting blank, and the like, are taken, so that the production cost of the steel plate is greatly lowered.