Today, financing the government's expenses through taxes is the most important and at the same time the most stable and with the least negative consequences on the economy and by adopting optimal policies in recession and inflation conditions, it can stabilize the economic conditions. Due to the extent of the government's obligations in the economic and social fields, the costs for the government have also increased and obtaining resources to cover these costs requires the implementation of ways to increase tax revenues. This paper deals with the modeling of the game between the taxpayers and the tax administration in order to achieve the factors affecting the optimal performance tax rate and also to determine the optimal performance tax rate. It is assumed that the income of the tax affairs organization (government) is distributed triangularly in the interval [0, 1] and the quality of the investigating group is not known to the taxpayers, then by solving the proposed game, the theorems have been presented. The results showed that the income of the tax affairs organization has an inverse relationship with the costs of the investigating and a direct relationship with the fines received from the taxpayers. Also, under certain conditions, the income of the tax affairs organization increases with the increase in the quality of the assessment groups and finally, the relationship between the optimal tax rate and the variables of investigating quality and diagnostic tax is inverse.
JEL Classification: C70, O11, C63, H21.