Abstract: Studies the languages that are independent of the L-prefix relation. The construction of the completion of codes are generalized as that of L-independent languages and on the other hand, the latter can be used to examine the former. In the completing process of codes the relation involved is bound up with the result of completion. It is therefore necessary to introduce various techniques into the process, and how they function can be expounded by the general construction of completion of L-independent languages. In this way a clear understanding is available to various methods of completion of codes.