Letters written in Dongba script are an important type of social documents in Dongba script. Two letters written in Dongba script to scholars have been published and translated before, but no letter of thanks written in Dongba script has been disclosed so far. This article interprets a recently written thanks letter in Dongba script, which can supplement the deficiency of such literature. From the contents of the thanks notes, it can be seen that Dongba culture has been revived in some places. In addition, some unusual writing forms of Dongba graphs appeared in this document, which can be used to supplement Dongba reference books when they are revised.

Expression type for mixed-use of Dongba characters can be divided into dominant type and parallel type. Causes for mixed-use includes three points: 1. similar or compatible patterns are the precondition for mixed-use; 2. certain relation exists among semantics of words represented by characters, or characters belong to the same classification in terms of meaning or have correlative meanings; 3. outcome is obtained during self-adjustment transitional stage of internal character of writing system. There are three solutions to solve the problem of similar characters: 1. re-distribution of characters’ functions; 2. integration of characters; 3. reconstruction of expression which is embodied in two aspects, including ideographical and phonetic expression transited from ideographical expression to additional phonetic complement, and transition from ideographical expression to pure phonetic expression.