The invention discloses an outer membrane mixed diamond spherical abrasive material and a preparation method thereof. The spherical abrasive material is composed of the following raw materials by weight percentage: 60%-80% of diamond abrasive, 10%-30% of a binder, and 5%-20% of an auxiliary material. The binder includes a mixture of thermosetting resin and water-based silica. According to the invention, the mixture of thermosetting resin and water-based silica is adopted as the binder, by means of simple heating and ultrasonic treatment, a high performance outer membrane mixed diamond spherical abrasive material can be prepared. The spherical abrasive material has the hardness and surface cutting force of ordinary diamond particles, and through combination of the thermosetting resin, water-based silica and the diamond abrasive, a resin cured film coated water-based silica structure can be formed, the single diamond combination particle brittleness can be changed, and the toughness and self-sharpness of the whole abrasive material can be improved. The outer membrane mixed diamond spherical abrasive material provided by the invention is especially suitable for ultraprecise grinding and polishing of magnetic heads, hard disks, optical glass and sapphire wafers of the LED industry.