Abstract: Word cloud is a popular text visualization technique that extracts keywords from text and displays them on the 2D space aesthetically.Word cloud is often used to display contents,aid text analysis and attract readers.In this work,the design space of word cloud is introduced from three aspects:visual encoding,layout and interaction.Then current word cloud design researches are summarized by four categories:semantic word clouds,shape-constrained word clouds,interactive word clouds and multi-document word clouds.Several works related to word cloud evaluation are also concluded.Finally,research challenges in semantic word clouds,shape-constrained word clouds,multi-document word clouds and Chinese word clouds,and suggest future work of word cloud visualization are discussed.