Abstract: Commercial ultra-fast cooling industrialized tests were carried out after high temperature final rolling of the Cr15 bearing steel bar by installing three ultra-fast cooling systems in addition to the original continuous rolling line in a special steel plant. The cooling rate was controlled by readjusting water pressure, nozzle size and the number of turn-on taps of water tanks after high temperature deformation of steel bar. The results showed that the C and Cr contents at the grain boundaries of secondary carbides are reduced with the size of pearlite pellets and the pearlitic lamellar gaps both decreased but the micro-hardness increases along with the continuously increasing cooling rate. Moreover, the cooling rate at anyplace on the cross section of the steel bar is available to restrain the precipitation of network carbides and transform all the overcooled austensites into pearlites. As a result, the class of the network carbides is lower than the grade II that is the professional standard.