The invention discloses a secondary cooling method and device of a high-speed small square billet or small round billet continuous casting machine. The method is concretely characterized in that a secondary cooling region is divided into a plurality of guide sections; a plurality of guide sections with the front ends connected with a crystallizer adopt closely arranged roller structures; the rest guide sections adopt single-roller support structures; then, the secondary cooling region is divided into a plurality of cooling sections; the plurality of cooling sections at the front end adopt water spraying nozzles for casting blank cooling, and the rest cooling sections adopt air mist spray nozzles for casting blank cooling. Through section division for corresponding arrangement, the casting blank secondary cooling technology is enabled to meet the requirement of high drawing speed; the problems of great bulging deformation, poor cooling intensity, poor cooling control precision, poor uniformity, high space region temperature returning and the like under the condition of high drawing speed are solved; particularly, the drawing speed is improved; meanwhile, the investment cost and the production operation cost of the continuous casting machine can also be obviously reduced; wide market and application prospects are realized.