The invention discloses a method for preparing a Ti/TiO2 or TiN biocompatible film on the surface of a magnesium matrix composite. The film has excellent biocompatibility, is tightly combined with the magnesium matrix material and can be used for stopping or delaying the corrosion of the magnesium matrix material in body fluid. If a Ti/TiO2 layer needs to be plated, the vacuum degree is above 3*10<-3> Pa through vacuumization, a pure titanium target is ignited for arc striking and discharging, and the deposition time is 2-10 minutes. If a TiN layer needs to be plated, nitrogen is introduced into a vacuum chamber, the arc striking current is controlled to be 50-100A, and the deposition time is 8-12 minutes. When the Ti/TiO2 or TiN film obtained by using the method is on service under a living body environment, the purpose of slowly degrading the magnesium matrix material can be reached, a chemical reaction between the magnesium matrix and the body fluid environment is effectively delayed, and the living body can discharge degradation products within a sustainable range; and the Ti/TiO2 or TiN film is a surface film which can be applied to magnesium matrix implant biomaterials and has biocompatibility.