The invention relates to a preparation method of a high-performance diamond reinforced Al-matrix electronic packaging composite material, belonging to the field of metal-matrix composite materials. The preparation method is characterized by comprising the following steps: adding alloy elements into a pure Al matrix to prepare elemental mixed powder or Al alloy powder; uniformly mixing the elemental mixed powder or the Al alloy powder and diamond single crystal grains according to the volume percentage ratio of 75:25-40:60; adding the mixture into a graphite mold for carrying out spark plasma sintering, wherein the mixture is added at the heating speed of 50-100 DEG C/min until the sintering temperature is 580-800 DEG C and the sintering pressure is 30-40MPa; keeping the temperature and the pressure for 5-20min; and obtaining the high-performance diamond reinforced Al-matrix electronic packaging composite material after the sintering process finishes. The alloy elements comprise B, Si, Cr, Ti, Nb, Ag, Cu and the like. The material of the invention has the characteristics that the heat conductivity reaches 430W/m.K, the heat expansion coefficient is 6.40ppm/K, the compressive strength is 331MPa, and the density is only 3.13g/cm<3>. The invention effectively solves the problem of graphitization of single crystal diamond grains in the preparation process of the material, and has simple preparation processes and high production efficiency.