Blank commercial instrument, also known as blank authorized bill, refers to the commercial instru-ment that the person who acts on commercial instrument only signs his name on the bill, and leaves the rest of items to be recorded, partly or even entirely, to other people to finish.And the supplementary right of the blank commercial instrument, terns out to be the central issue in this field.Since the supplementary right of the blank commercial instrument is a civil right, we can analyze it in the civil law perspective.About its theo-retical basis, there are mainly four doctrines:theory of appointment, theory of agency, theory of contract, and theory of authorization.After compare these theories and the supporters’ point of view of each other, we can draw a conclusion that the theory of authorization is the most appropriate one.Finally, concerning the type of the right, we find that it is a dilemmatic situation between admitting that the supplementary right of the blank comme