The invention discloses an unstructured data asset reveal prevention method based on hierarchical classification. The method comprises the following steps: a, classifying unstructured data asset by a controlled terminal, and carrying out digital signature; b, when the controlled terminal requests to send unstructured data to the Internet or Extranet, filtering the data by a network protection server through mirrored flow and sensitive keywords; c, if the unstructured data includes sensitive keywords, verifying the signature of the unstructured data by adopting a public key of a corresponding sensitivity level; d, if verification is passed, blocking the request of the controlled terminal of sending data to the Internet or Extranet. According to the invention, the method that the keyword filtering and data signature are combined is adopted to protect unstructured data in the classified data asset of an enterprise, so that data leakage can be prevented effectively and the phenomenon of the misinformation of information protection is reduced.