The invention belongs to the field of nanometer materials, and discloses non-wood material nanocellulose and a preparation method and application thereof. The preparation method of the non-wood material nanocellulose comprises the following steps: mechanically pulverizing at least one of the non-wood materials like wheat straw, rice straw, maize straw, Chinese alpine rush and sugarcane bagasse, collecting a material powder passing through sieves, collecting the material powder capable of passing through a 60-mesh sieve but incapable of passing through a 80-mesh sieve, then putting the materialpowder into an alkaline liquor with a proper concentration, enabling the material powder to react for a certain period of time in a reaction kettle of 90-150 DEG C, then taking out the material powder, filtering, washing till the solution is neutral, then homogenizing to obtain the non-wood material nanocellulose. The preparation process of the non-wood material nanocellulose is simple, and the operation is convenient. The non-wood material nanocellulose is excellent in physical and mechanical properties and biocompatibility, and can be applied to the fields of flexible electronic devices, biological and medical materials and the like.