The invention relates to a preparation method and application of a {010} high-energy facet exposed BiOCl nanosheet. The preparation method comprises the following steps of uniformly mixing a bismuth source, a chlorine source and an alkali source according to a certain ratio, applying the mechanical force of high-energy ball milling to chemical reaction, then performing heat treatment at 200-600 DEG C, and then performing impurity removal with washing, solid-liquid separation and drying to prepare BiOCl nanosheet. The prepared BiOCl material is formed by a nanosheet with the thickness being 5-50nm and the side length being 150-250nm, and the {010} facet exposure degree is 60-90 percent. The preparation method has the advantages of simpleness in preparation technology, easiness in realizingindustrial production, low cost of the preparation technology, environmental protection and the like. The prepared {010} high-energy facet exposed BiOCl nanosheet is widely applied to the fields of super capacitors, alkaline storage batteries, lithium ion batteries, photocatalysts, pearlescent pigments and medicines and the like.