The invention provides a preparation method for a nano injection molding composite material. The method sequentially includes the following steps of mechanical pretreatment, two-step pre-etching, primary DC electrified corrosion, secondary dipulse electrified corrosion, aftertreatment, drying and nano injection molding. Ultrasonic assisted corrosion happens in the electrifying process. A base material of the composite material refers to one of aluminum alloy, titanium alloy, magnesium alloy or stainless steel. The preparation method for the nano injection molding composite material can be applied to preparation of mobile communication terminal shells.