The invention discloses a file encryption and decryption method based on combinatorial coding, belonging to the field of information safety and solving the problem of poor confidentiality of the existing file encryption and decryption method. The file encryption method of the invention comprises: according to all secret key sequences solved by an initial secret key, carrying out whole arrangementon data in a grouped sequence for encryption in each round to form a dictionary space and calculate out an ordinal number; then, according to the rule, splicing a new sequence; after all groups of the secret key sequences in the round are performed with circulated splicing, carrying out xor with a new sequence; replacing elements front and back for an encryption file formed in an odd round; and finally encrypting the file after four rounds of encryption. The decryption process is the inverse process of encryption, and comprises the following steps: in the add round, replacing the elements front and back; then, carrying out xor with a key sequence obtained after circulated splicing secret key; adopting an exhaustive method to successively solve the elements of the grouped sequence; splicing m numbered solved grouped sequences and remainders to serve as a file to be decrypted; and finishing decrypting after four rounds.