Abstract: Tool materials were prepared by adding different silicon contents in M2 machining high speed steel. The test and analysis of cast microstructure and casting properties of samples were carried out. The results show that with the increase of silicon content, the microstructure of the sample is refined first and then coarsening, the fluidity of the sample is basically unchanged and then decreases dramatically, and the hot cracking resistance of the sample increases first and then decreases.Compared with those of M2 high speed steel without silicon, the flow length of the liquid steel with 0.5% and 1.0% silicon has no obvious change and the fluidity of the sample is basically unchanged; when the silicon content increases to 1.5 %, the flow length of the liquid steel decreases by 9.89% and the fluidity of the sample is obviously worse. Compared with those of M2 high speed steel without silicon, the crack length of the steel with 1.0%Si decreases by 48.21%, the hot cracking resistance of the sample is the best.