Based on the forecasts of the fourth five-year development plan of Iran, the current government expenditures have to be financed through non-oil resources. But according to realized statistics of the plan's performance, the ratio of the total tax over the total government expenditures is about 36 percent on average. This means that the Iran's government and tax authorities are faced with a budget challenges in achieving the budget targets. Although having the effective tax policy is important to achieve the tax targets, designing the tax policy is a difficult and complex task and it requires the various tax stakeholders' cooperation in the whole economy, while they have different subjectivity and opinions about the designing of the tax policy and its effects on the economy.
In this paper, the Delphi method is used to model the whole decision makings involved in designing tax policy and the fuzzy theory notions are applied for modeling both the linguistic variables and imprecision of the experts' views. Based on the Fuzzy Delphi method, the most effective tax policy is designed and developed when it incorporates imprecision and subjectivity into the model formulation and solution process.