Although it is well known that Ewald2D summation is the choice for simulating 3D system with 2D periodicity,development of an efficient algorithm for Ewald2D summation lays far behind that of Ewald3D type algorithms(such as PME).The first successful algorithm with enough accuracy and reduced computation cost is developed in 1999 by Yeh and Berkowitz,in which they used a dipole term to explain the surface effect.Based on this,Arnold and co-workers in 2002 invented the Ewald ELC method to do the same work but more accurately,in which the excess electrostatic layers affections are excluded.To some extent,both methods generate the similar results with the original and exact Ewald 2D method.Here,we try to explain the intrinsic connections between different methods mathematically,and naturally give another method with precise error bounds and extensive application.The calculations of a ionic crystal model and simplified BTB molecule model will be presented.