Among the current studies of the effect of topic familiarity on incidental vocabulary acquisition (IVA) in reading, reading has long been seen as a tool to achieve the experiment and reading performance has not been taken as a possible independent variable in the research. In view of this, this paper, with the help of Path Analysis in SPSS 17.0, explores the relationship between topic familiarity, reading performance, and L2 incidental vocabulary acquisition. It is found that topic familiarity has a significant influence on reading performance and reading performance has a significant effect on vocabulary learning. Specifically, topic familiarity has an indirect influence on IVA but reading performance has a direct significant effect on it.