The elastic-plastic finite element mechanical model of hypereutectic Al-Si alloy was established based on ANSYS software. When the Si particles were circle, trapezium, rectangle or triangle, the microstress of Al-Si alloy under the external load were simulated. When the size of Si particles changed from 25μm to 45μm, the stress of Si particles and matrix interface was calculated. The effects of morphology and size of Si particles and loads on micro-mechanics characteristic of alloy were analyzed. The results showed that: under the same load, triangle or wedge angle Si particles make the biggest stress in the matrix, trapezoidal particles make the second and the spherical particles make the smallest. With the increase of the load, the stress and the stress concentration of Si particles in the matrix was increased, the stress of wedge angle particle increases remarkably, but the stress of spherical particles increases slowly. With the increase of the size of Si particles, the stress and the stress concentration of Si particles in matrix are increased.