The invention discloses a convex mirror shaped silicon nanosheet material, and a preparation method and an application thereof. The convex mirror shaped silicon nanosheet material is thick for the middle and thin for the edge, is similar to the shape of a convex mirror, and has the thickness of less than 5 nm and the transverse size of 50-150 nm. The preparation method comprises the steps of 1, carrying out layer insertion and separation: carrying out layer insertion to increase the distance between a silicon layer and an aluminum layer in montmorillonite, and carrying out ultrasonic oscillation to destroy a bonding force between the layers to separate the silicon layer from the aluminum layer; 2, carrying out magnesiothermic reduction to obtain solid mixtures such as a silicon nanosheet and the like; and 3, carrying out acid pickling and impurity removal to obtain a convex mirror shaped silicon nanosheet. The preparation method has the advantages of easily available raw materials, lowcost and simple preparation process; and the obtained convex mirror shaped silicon nanosheet can be used as a negative electrode material of a lithium ion battery, and has relatively excellent electrochemical performance.