As a new product in the digital era, GIF (Graphics Interchange Format) poster has shown great potential in online advertising due to its expressive form, informative nature, interactive design, and high communication efficiency. Based on the synthetic theoretical framework for multimodal discourse analysis and supplemented by visual grammar theory, this study explores the meaning construction and communication effect of advertising of online GIF poster One Call Away. The research shows that ideology provides the prerequisite for understanding GIF posters and realizing communication effect of advertising at the cultural level. Contextual factors serve as motivation for the formation of GIF posters’s strengths and communication effect of advertising. As far as the content is concerned, the communication effect of advertising is determined by the use of multimodal resources in meaning construction. At the expressive level, GIF format files provide technical support for realizing communication effect of advertising in reality. The multimodal discourse analysis of online GIF posters with advertising knowledge aims to provide linguistic explanations for advertising communication effects of GIF posters.