Abstract: An in-situ reaction pathway of particles was designed according to the formation temperature of TiB₂ and TiC in-situ particles, and TiB₂ and TiC dual-phasic particles were prepared in Al-xSi-4.5Cu（x=7,12,18, wt%） cast alloy melt. The microstructure of the prepared composite was observed by using optical microscopy（OM）, scanning electron microscopy（SEM） ＆ energy-dispersive spectroscopy（EDS） methods, and the Vickers hardness was also tested. The influence of Si content of the matrix alloy on the distribution of in-situ TiB₂ and TiC particles and the hardness of the composite was investigated. The results show that TiB₂ and TiC dual-phasic particles in micro-nano size are obtained in the composite with the three Si contents by in-situ synthesis method. As the amount of Si increases, the tendency of in-situ particles distributed around Si phase is more aggravated. The hardness of TiC-TiB₂/Al-12Si-4.5Cu reaches the maximum of 173.56 HV. However,when the Si content increases to 18wt%, TiC particles are not stable and decompose, which leads to a decrease in the hardness of the composite.