Abstract：Based on the frequency table of meaningful trigrams of BLC, 171 highest-frequency threeword lexical chunks are identified and are used as referent target chunks. Then these target chunks are also identified in English majors' business letter writing. Comparative studies show that the output rates of nearly 60% of the target chunks in the students' letter writing are lower than their occurrence rates in BLC. Some problems in students' use of those chunks are as follows: low output rates of sentence builder chunks; over output of chunks with “we”; and inadequate output of chunks with modal verbs.

Keyword：BLC;Business Letter Writing;three-word lexical chunk;output;