Abstract. Value Added Tax (VAT) is an indirect tax which is paid by buyer along with purchasing of goods and services. Then the seller is obliged to transfer it to treasury of state. In comparison with other common taxes, Value Added Tax (VAT) is a new tax system with efforts of economists for remove / reduction of any disorder or shortages in traditional taxes and also income increase of the state. We intend, in this research, to find out any obstacles for complete implementation of VAT system in Iran. For this purpose we used a standard and confirmed questionnaire with Chronbach’s alpha (reliability coefficient: 0.899) submitted to 80 persons of tax experts. According to the results of one sample t-test, some minor external factors, major external factors and internal factors prevented from complete implementation of tax system on value added in Iran. Furthermore according to the results out of fuzzy network analysis it is obvious that from among all these factors we have traditional payment methods of commercial interactions by tax payers, imposing of administrative/financial costs for tax payers for respecting legal necessities of VAT system and also lack of a compatible accounting system with VAT system for tax payers had the most obvious roles in lack of complete implementation of VAT system in Iran.