Abstract: A magnesium alloy matrix composite was fabricated by squeeze cast with the preform made of crystallized aluminum silicate short fibers as reinforcement and aluminum phosphate as binder. The reaction products were investigated by optical microscopic, XRD and SEM, and the chemical reaction at the interface between the short fiber and matrix was analysed by thermodynamic analysis. It is shown that the alumina silicate fiber can be chosen as the reinforcement of Mg matrix composites, and an ideal stronger interface was formed by the chemical reaction between magnesium alloy matrix and aluminum phosphate binder due to the produce of MgO particles and a little MgAl₂O₄ particles. In addition, a brittle Mg₂Si phase was precipitated at the interface through the reaction between amorphous SiO₂ and Mg in the magnesium alloy matrix, which affects the mechanical properties of the magnesium alloy matrix composite.