Three methods such as potential superposition，integration interval transformation and doping moment，are introduced to calculate the potential induced by one-dimensional arbitrary charge distribution，taking a MOS structure with non-uniformly distributed oxide charges as an example. The equivalence of the three methods is verified. As a focus，the doping moment method is employed in C-V characterization of a non-uniformly doped n+p junction and threshold voltage calculation of MOSFETs with a non-uniformly doped channel. The principles of varactors and retrograde doping in MOSFET are discussed.