The tool-based code review is a light-weight variant of traditional code review for software quality assurance. Due to the asynchronous collaboration of tool-based code review, developers risk submitting patches that attempt to achieve similar objectives (defined as similar patches in the study), which is prone to waste extra efforts for developers. In this study, I conduct an empirical study to address the following points: (1) understand the impact of similar patches on reviewing efforts. (2) analyze whether or not textual information is important in detecting similar patches (3) investigate whether or not the existing detection techniques can work well on similar patches.