Objective: This article is the first time to use computer model tools to discuss transcranial direct current stimulation（tDCS）forclinical treatment problems, applying ROAST（Realistic volumetric-approach to simulate transcranial electric stimulation）to the analysis of the influence of electrode position errors in the tDCS clinical treatment, and quantitatively analyze effects from the position offsets. Methods: The article takes F3 and F4 as an example to treat depression, simulates and calculates the electric field dose excited in the intracranial target area, compares the influence of the electrode position errors on the intracranial treatment target electric field dose, and gives the electric field dose variation curve under application of 2 mA and 4 mA current. Results: The simulation shows among 32 kinds of physical position errors, the pad electrode and the disk electrode cause the electric field dose to vary from -10.3% to 72.4%, -12.9% to 11.3%, both decreasing and increasing; this result is due to the non-uniformity of the cerebral cortex. When the electric field dose is reduced, the electric field in intracranial target area will be low than the effective electric field dose, so it is possible that the clinical treatment effect of tDCS may not be good. The simulation also shows that when 4.0 mA is applied, the intracranial target area will produce an effective electric field dose. In addition, the variation of the electric field dose generated by 32 kinds of error positions in the intracranial target area is basically the same as that when 2mA is applied. The degree of electric field dose change is consistent with the magnitude of the applied current It's roughly okay. The degree of electric field dose change is roughly irrelevant to the magnitude of the applied current. Conclusions: The results and methods of this study can be used to find the individual dose optimization of tDCS for clinical doctors.