<p>Translation naturalness is a pivotal criterion of translation quality and is defined herein as linguistic conformity to the target language. Despite its significance in translator training, exactly how it is measured, appraised or achieved is less clear, hampering the efficient development of student translation competence. A corpus consisting of 1800 sample Chinese to English translations by students, professionals and native English texts in fiction, magazine and news genres was compiled to assess the naturalness of student translations and provide pedagogical guidance based on the empirical evidence. Adopting a factor analysis method, this study formulated five dimensions out of 34 linguistic features encompassing nominal versus verbal expression, difficulty versus easy words, diverse versus identical words, complex versus simple sentence and more versus fewer clauses to measure and explain naturalness variation in student translations, relative to professional ones and native texts. The findings confirm the efficiency of the five dimensions in assessing the naturalness of student translations in groups and in individual. Furthermore, the findings empirically validate the influence of genre variation, the existence of tolerance to unnaturalness, and the phenomenon of unbalanced translation competence. Finally, this study synthesizes the findings into concrete implications for genre specific translation naturalness assessment in the educational context to enhance objectivity, generalisability, and pedagogical efficacy.</p>