The invention discloses a method for preparing an anti-ablative coating of a carbon-based composite material. The method is characterized by comprising the following steps: polishing burr on the surface of the carbon-based composite material by using sand paper, performing ultrasonic washing in acetone, subsequently baking, putting the dried carbon-based composite material into a vacuum chamber, wherein the pressure is less than 5*10<-3>Pa, introducing an Ar gas to be 2-4*10<-1>Pa, washing the surface of the carbon-based composite material by using an ion source with bias bombardment, preparing an SiC layer in the presence of argon when the pressure is 0.2-2.0Pa, the bias pressure is 50-200V and the SiC target power is 4-12A/cm<2>, and preparing a ZrB2-MoSi2 coating under the conditions that ZrB2-MoSi2 powder is taken as a thermal spraying material, the spraying voltage is 60-70V, the spraying pressure is 10-100kPa, the spraying current is 600-700A, the argon flow is 35-45l/min, the hydrogen flow is 5-15l/min, the argon flow in feeding the powder is 2-4l/min, the powder flow is 5-30g/min, and the spraying distance is 100-300mm. The coating disclosed by the invention has the characteristics of high binding strength, excellent flashing resistance and remarkable high temperature protection effect for the carbon-based composite material.