In this thesis, we design a 2-D device simulator to simulate the triple gate’s potential distribution and electron distribution , then discuss the corner effect of triple gate’s structure. We add Poisson’s Equation to analyze 2-D potential distributions and simulation, using the formula to compare with the simulation, and use the formula to obtain threshold voltage. In order to understand the characteristics I_D-V_G of device and subthreshold swing and DIBL characteristic, we add 3-D device simulator to analyze the short channel effects about triple-gate structure.