This paper presents an Optimality-theoretic account of word stress in Chinese-English interlanguage. The OT-L2 model states that L2 acquisition is a re-ranking process from L1 state towards L2 state. There are three constraints concerned in this study: Parse-syllable, WSP and Nonfinality. The L1 ranking is Parse-syllable>> WSP, Nonfinality and the L2 ranking is Nonfinality, WSP>> Parse-syllable. Three interim stages predicted in Chinese-English interlanguage are tested in a perception experiment of pseudo-words. The results support the patterns and order of interim stages that is predicted by one of the re-ranking scenarios. On the other hand, the pattern predicted in the ranking of WSP>>Nonfinality, Parse-syllable is not attested in the data. This indicates that the actual pattern of development is more restricted than predicted by the OT model.