Earlier bibliometric research on the relationship between author ethnic diversity and scientific impact has found a positive relationship between these two variables. However, more research is needed to understand the reasons for this effect. To further explore how ethnic diversity affects scientific impact, this study put forward a model to connect ethnic diversity with scientific impact, assuming novelty and audience diversity as mediators, using structural equation modeling (SEM). We find that ethnic diversity can increase scientific impact when not considering affiliated country diversity and affiliated country size (in terms of publication output), but that ethnic diversity does not have any effect on scientific impact when taking the two variables into account. Earlier studies have found that ethnic diversity can increase scientific impact, which might be due to the fact that these studies did not control for affiliated country variables. When not considering affiliated country variables, ethnic diversity seems to promote short-term scientific impact rather than long-term. Our research further suggests that ethnic diversity can generate scientific impact via audience diversity.