For the communication parties which only have file exchange and no other means of information exchange, this paper proposes a design method of a point-to-point ordered reliable data link layer. Control information is appended to the exchanged files to realize the basic link control function. Mechanisms of sliding window and timeout retransmission are also introduced to address the problem of disorder and even loss. Furthermore, MD5 or some other check codes are also appended to the exchanged files to achieve an efficient verification of possible damage, guaranteeing the integrity and consistency of the exchanged files. The practical application shows that ordered reliable communication link service can be realized as long as all appropriate sliding window parameters could be found, even though the communication parties only have the means of file exchanges.