The present study proposes a source speech register analysis model that incorporates textual and situational components and parameters of register equivalence in the target language to identify the relations between the source language register and student interpreter’s performance, textual register mismatch between the source and target languages, and the relevance between register equivalence parameters in the target language and interpreting quality. The findings are as follows: first, source language register does have influence on interpreter’s performance, and relations exist between the two. In general, higher source language register brings better interpreting quality. Three assessment criteria and the overall quality differ across different levels of registers in the source language. Second, register mismatch between the source and target languages happens since interpreters are inclined to lower the register of interpreting output from the high-register source speech and increase the register level in the target language in the case of the low-register speech. Third, intonation and voice have the highest correlations with the interpreters’ performance. Fluency ranks the second, and lexical-semantic choices the third.