The invention relates to a method and a device for secondary quenching of high-carbon cast steel slot or high-carbon cast steel grit, wherein the device for the secondary quenching is provided with a nozzle at the feed port of a furnace pipe; the nozzle is connected with an air inlet valve and a fuel oil and fuel gas valve through pipelines; one end of the discharge hole of the furnace pipe is provided with a flue outlet; and the discharge hole of the furnace pipe is connected with a cooling quenching unit. The method comprises: adding semi-finished products of as-caststate high-carbon cast-steel slot into the device for secondary quenching and heating to 800-900DEG C and preserving the temperature for 1-60min, and then feeding the obtained product in the cooling quenching unit for cooling. The obtained high-carbon cast steel slot or high-carbon cast steel grit of the invention can eliminate ingredient segregation, improve ingredient uniformity and uniformity of hardness, reduce skin decarburization, improve shock resistance and abrasion resistance, and prolong the service life by 10-30% compared with the product of the existing high-carbon cast steel slot under the equal hardness.