Based on a self-built corpus of English compositions by Chinese English majors， this paper explored the features of SO and some of its collocations in L2 writings from the dimensions of frequencies， register， colligation， and semantic prosody compared with those in the English native speakers'( NSs) corpus． This study has found SO was overused in L2 writings， but with the development of their English proficiency， the frequencies of SO and its typical collocations were reducing and getting closer to the use of the NSs． The study has also found that the register features of SO in composition had salient spoken English features， that the patterns of colligation were significantly different from those of the NSs， and that the semantic prosody was similar with that of the NSs， but with some differences．