Abstract: The microstructure and properties of in situ VC_P/steel composite fabricated by casting are investigated, and the formation mechanism of the composite microstructure is also analysed. The results show that in situ VC_P /steel composite has low pouring temperature (1723~1773 K) and good cast forming. It is suited to fabricate the in situ composite that demands a large reinforced particle volume fraction. In situ VC_P composite contains fine VC particles, which distribute homogeneously in the matrix, and 15 % particle volume. Three types of reinforced VC phases, granular VC from melt, strip eutectic VC, and granular VC separated from matrix, were found in composite microstructure. The composite microstructure stability can be remarkably improved by alloying matrix. After 923 K temperature, the composite can still hold hardness at HRC 60. This property can improve the composite wear-resistance at high temperature.