By the end of June 2015, the number of Chinese online shopping users has reached 374 million, which makes up 40.7% of all the internet users. Online shopping has become one of the most popular activities online. The rapid development of online shopping market has also made the influencing factors of online shopping become the focus of researchers. Just like in real life, others’ comments play an important role in the decision-making process of online shopping. Relevant research have found that: all the comprehensive score, timeliness, quantity, quality and valence of online reviews, as well as the credibility of reviewer could affect individuals’ purchase decision online. As the most important attribute, the quantity and quality of online reviews get more attention. Though many studies have revealed that both of them had positive effect on purchase decision, there is still a dispute about the relative effect size. With the deepening of research, researchers are more and more inclined to think that the impact of online reviews on purchase decisions is essentially a process of processing and accepting the review information, and the Elaboration Likelihood model (ELM) is also applied to this field. This theory pointed out that attitude change may occur via two routes of influence: the central route and the peripheral route, and these two alternative routes differ in the amount of thoughtful processing of information or “elaboration” – the intensity of motivation and the ability to process the information. This theory explains why people will be differently affected when they are facing the same information. Based on this theory, studies have found that the product category and involvement affected purchase intention through different information processing motivations and routes, and they could moderate the impact of online reviews on product sales. And need for cognition is an important reflection of individuals’ different information processing motivation. Therefore, this study aimed to explore the impact of online reviews’ quality and quantity on online purchasing intention and its mechanism under the perspective of ELM. A between-group experimental design of 2 (quality of online reviews: high vs. low) × 2 (quantity of online reviews: more vs. less) × 2 (level of need for cognition: high vs. low) was adapted. To guarantee the ecological validity, the reviews were first selected from a real shopping website, and then were evaluated to select out the reviews of high and low quality; as to the quantity of reviews, there were 12 for more quantity group and 2 for less quantity group; and participants were categorized as high or low in need for cognition via a median split. A total of 320 undergraduate students participated in the online experiment. The results showed a significant main effect of review quality and a significant main effect of review quantity. Also, the results showed a significant review quality × need for cognition interaction and a significant quantity × need for cognition interaction. Further simple main effect test showed that individuals with high need for cognition would be affect by the quality of the online reviews, while individuals with low need for cognition would be affected by the quantity of online reviews. This study deepened the research on online reviews’ impact on purchasing decision.