Online reviews, especially additional reviews, have become an important channel for consumers to obtain information about product quality. Based on review data obtained from “AutoHome”, which is a most popular car review platform in China, this study explores the influence of additional review function on the initial reviews from both the reader and reviewer levels. At the reader-level, the introduction of the additional review function improves readers’ perceived usefulness of the reviews. At the reviewer-level, it can drive reviewers to write more initial reviews. In general, the introduction of such a function can be regarded as an improvement of the existing review mechanism. The findings of this study can not only enrich the research on online word-of-mouth, but also provide valuable reference for related practitioners.