Price and promotion strategy have been widely discussed in multichannel retailing, but little study was focused on the promotion strategy in the context of multiple platforms. Through transaction data from a company's different platforms, our study investigated the impact of promotion integration strategy on company's overall sales performance on different platforms. Combined with platform's index data about product market demand, the moderating effect of platform's market demand was further evaluated. Using a fixed-effect model, our research found the positive effect of promotion timing integration and the negative effect of promotion depth integration on sales performance. We also found the moderating effect of platform's market demand. Thus, our study generates important theoretical and practical implications for managing promotion activity on multiple platforms.