High-speed steel M2 strip has been experimentally produced by using a twin roll strip castor. The microstructure of the strip and the eutectic carbide in the cast-rolled strip were examined in detail. The spheroidizing procedure of the eutectic carbide in the twin roll cast M2 high-speed steel strip was investigated with the method of annealing, quenching and tempering. The results show that the eutectic carbide was gradually spheroidized with the increase of heating temperature and holding time through coarsening and accumulation of eutectic carbide, dissolving and breaking up of net work eutectic carbide, and precipitating and coarsening of secondary carbide. The kinetics analysis of coarsening and accumulating of eutectic carbide, and coarsening of secondary carbide in the high-speed steel strip were made based on the experimental results, and the growing transient velocity equations of carbide were deduced. The mechanism of cast-rolling enhancing the spheroidizing of eutectic carbide in M2 steel was discussed.