With the rapid growth of the number and diversity of web APIs on the Internet, it has become more and more difficult for developers to look for their desired APIs and build their own mashups. Therefore, web service recommendation and automatic mashup construction becomes a demanding technique. Most of the researches focus on the service recommendation part but neglect the construction of the mushups. In this paper, we will propose a new technique to fast and accurately build a API network based on the API’s input and output information. Once the API network is built, each pair of the connected APIs can be seen as generating a promising mushup. Therefore, the developers are freed from the exhausting search phase. Experiments using over 500 real API information gathered from the Internet has shown that the proposed approach is effective and performs well.