The invention discloses a micro-refining production method of Q235b-grade steel. The micro-refining production method comprises the following steps of primary smelting, LF refining and continuous casting, wherein in the LF refining process, the content of carbon in molten steel is controlled to be 0.13-0.19%, the content of silicon in the molten steel is controlled to be 0.10-0.30%, the content ofmanganese in the molten steel is controlled to be 0.25-0.75%, the content of phosphorus in the molten steel is controlled to be smaller than or equal to 0.035%, the content of sulfur in the molten steel is controlled to be smaller than or equal to 0.025%, the content of aluminium in the molten steel is controlled to be 0.005-0.010%, and the mass ratio of manganese to silicon is controlled to range from 2.5 to 3.0. According to the micro-refining production method, in the LF refining process, carbon, silicon, manganese, phosphorus, sulfur, aluminium and the like in the molten steel are optimized, and therefore the problem of the pourability of the Q235b-grade steel is solved, the calcium treatment is effectively reduced, the production cost is obviously reduced, and the use requirements ofusers are met. By adopting the micro-refining production method, the production cost of the steel is reduced by 12-14 yuan per ton.