【Purpose/significance】In recent years, violent terrorist activities all around the world display the characteristics of devastating, larger influence, strong planning and various measures. Terror threat warning becomes the most important work to fight against terrorism. Data mining technology plays an important role to accomplish terror threat warning. Data preprocessing is the basis of all data mining technologies.【Method/process】This paper proposes how to make data preprocessing in the field of counter terrorism intelligence quantitative analysis. Four types of preprocessing methods, including data cleaning, data integration, data discretization and data dualization, are discussed to deal with terror related information. All fundamental data are based on public reports.【Result/conclusion】These preprocessing methods could eliminate data defects and provide standardized data for next data mining step to show mining conclusions and visible results.