Computerized Adaptive Testing (CAT) is a new testing mode that utilizes the adaptive measurement concept of ”tailored to fit.” Compared with traditional paper-and-pencil testing, CAT has the advantages of improving measurement accuracy, reducing test length, and ensuring test security. Therefore, it is highly regarded by researchers and practitioners both domestically and internationally. However, the platform construction of CAT involves complex statistical measurement theory and tedious numerical calculations, which hinder the application and promotion of CAT in practice. This article mainly introduces the development platform of computerized adaptive testing - flexCAT. Users can quickly build their own CAT system using the convenient human-computer interactive interface provided by the flexCAT platform. This article will introduce the first web-based computerized adaptive testing development platform in China - flexCAT, from the perspectives of its advantages, basic theory, module functions, etc. The aim is to provide free adaptive testing platform development services for research and application personnel in the fields of education, psychology, and further promote the development of psychological and educational measurement theory and technology in China. The URL for the flexCAT platform is: http: //www.psychometrics-studio.cn/app/cat demo/index.html?Id=false&Block=false.