The invention relates to a high-strength fine grain rebar which contains the following chemical components according to mass fraction: 0.15-0.45% of C, 0.5-1% of Si, 1-2% of Mn, 0.005-0.025% of P, 0.005-0.025% of S, 0-1% of Cr, 0-0.1% of V, 0-0.5% of Mo, 0.005-0.025% of Ti, 0.001-0.006% of Ca, 0.002-0.006% of O, and the balance of Fe and impurity elements. A preparation method comprises the following steps: (1) smelting molten iron and/or steel scrap into molten steel and performing deoxidation alloying; then performing LF refining; and performing all-protected casting, to obtain a casting blank; (2) heating and preserving heat; (3) performing rough rolling and finish rolling on the casting blank; and (4) cooling to obtain the high-strength fine grain rebar. According to the invention, byco-improvement of the smelting technology and the rolling technology, cheap alloy elements and oxysulfide inclusions in steel are sufficiently utilized, so that grain size is refined, strength is improved, and the low-cost and high-efficiency production of the high-strength rebar is realized.