在本篇論文中,我們採用圓柱座標下的梯形網格當做探討依據,並且進行一系列的PN 二極體模擬。首先,我們推導在圓柱座標下的PN 二極體的電位、電場、空乏區寬度等公式。並以二維等效電路模擬來驗證其正確性,並且,探討在PN 陡峭接面下之崩潰電壓的特性公式並且以二維的等效電路來驗證。其結果驗證模擬值與理論值相符。 In this thesis, we use the cylindrical coordinates to substitute Cartesian coordinates to analyze and simulate the circular PN junction. First we develop the analytical equations for electric potential, electric field, depletion width and others for the circular PN diode. We use 2-D simulations to verify the validity of the analytical equations. Also, we develop the analytical breakdown voltage and compare with 2-D simulations . The developed equations are in good agreement with 2-D device simulations.