By means of Gleeble-1500 dynamic thermomechanical simulator,the continuous casting process for HRB335C steel was simulated using solidifying method and hot ductility and strength of the steel were determined. The test results indicate that there are three temperature regions of brittleness for HRB335C billet in the temperature range from 700℃to solidification point;the first temperature region of brittleness is 1 300℃to solidification point of the billet, the second temperature region of brittleness is 1200-1000℃,and the third temperature region of brittleness is 700-850℃;the steel is plastic at 850-1000℃.The cracking sensitivity was studied in the different temperature zones of the brittleness for steel HRB335C and the target surface temperature curve for the secondary cooling is determined. With optimized process,the mathematical model of the steady temperature field with two-di- mensional heat transfer for 150 mm×150 mm HRB335C steel billet was established to optimize the secondary cooling process. The conic relation of water distribution between secondary cooling water flux and casting speed is re- gressed. Keeping the surface temperature of billet before the straightening point above 1000℃, the results of billet test indicate that there is free central shrinkage cavity. The billet defect is decreased greatly, and the quality of billet is obviously improved. The test results indicate that that are three temperature regions of brittleness for HRB335C billet in the the first temperature region of brittleness is 1 300 ° C. to solidification point of the billet, the second temperature region of brittleness is 1200-1000 ° C., and the third temperature region of brittleness is 700-850 ° C. ; the steel is plastic at 850-1000 ° C. The cracking sensitivity was studied in the different temperature zones of the brittleness for steel HRB335C and the target surface temperature curve for the secondary cooling is determined. With optimized process, the mathematical model of the steady temperature field with two-di- mensional heat transfer for 150 mm × 150 mm HRB335C steel billet was established to optimize the secondary cooling process. The conic relation of water distribution between secondary cooling water flux and casting speed is re-gressed. Keeping the surface temperature of billet before the straightening point above 1000 ℃, the results of billet test indicate that there is free central shrinkage cavity The billet defect is decreased greatly, and the quality of billet is obviously improved.