This study,developing and piloting a questionnaire as an instrument, using relevant statistical procedures, investigated the extent to which the essay in TEM8 (TEM8E) is a valid test in terms of theory-based validity. The research design mainly involved student participants from three universities in China. The findings of this study may suggest that the ability in writing tested could be generally reflected by the internal sub-processes; the test-takers' translating ability variance can be marginally statistically reflected; the sub-processes such as topic and genre modifying, organizing, translating, reviewing may have more effect on score gains than some other sub-processes. In this sense, TEM8E can be generally regarded as a test reflecting the writing ability, but it needs improving.
