This application relates to a separator, including: a substrate; and a coating layer provided on at least one surface of the substrate; where the coating layer includes inorganic particles and organic particles, the organic particles include first organic particles, the first organic particles are embedded into the inorganic particles and form bulges on a surface of the coating layer, and a number-based median particle size of the first organic particles is ≥12 μm. This application further relates to a method for preparing the separator, a secondary battery containing the separator, a battery module including the secondary battery, a battery pack, and an apparatus.