This study aims to identify what professional interpreters would do when they face the risk of fluctuations in speech rate in simultaneous interpretation. In order to investigate it, the study first proposed the method of calculating the speech rate, information density as well as the percentage of interpretation. Then, it gathered research materials which can be classified into two types, one is speakers speaking with text and the other is impromptu speech. On top of that, the study analyzed how the speech rate, information density and speech pattern of speakers affected the percentage of interpretation, and what the most suitable new information is for professional interpreters.