Business tax revenue is the main source of government income. It is also top ranked in terms of tax evasion. Such a problem has badly affected government’s tax revenue. The goal of this thesis is providing a decision to build a detection system for fictitious companies. In order to reach the goal, we collect data and analyze data source in a specific procedure from tax system which is made by a specialist. Building an effective detection system using business Intelligence technology is the next stage, and hope to achieve in advance against sales tax evasion and avoidance.