From above mentioned problems, it is necessary to study the power of assessment officer under the Thai Revenue Code for implementation of taxation. The authority to assessment increase tax of Board of Appeals to determine the scope of the authority follow the legal provision. If there is no provision of law about tax authority it will affect the efficiency of tax collection and the damage to the state also affecting taxpayers or not? and what is the solution should be solve the problem, how it should be for tax authority effectively executed so that the officer of the Revenue Department actions tax authority effectively. And promoted the overall public benefit with fairness within the framework of law principles,Legal interpretation according to rule of law