In this article, a full-domain harmonic potential balance (HPB) model, which is free of subdomain division and cumbersome geometric transformations, is presented for 2-D magnetic field analysis of electrical machines. The key contribution is the proposed HPB equation, by which the harmonic distribution of magnetic vector potential in electrical machine is solved. To achieve this result, the singularity functions are applied to realize a global modeling. Then the full-domain magnetic vector potential distribution equation, which implies the boundary conditions, is established. For radial-flux electrical machines with 2-D annular domain, the logarithm-translation mapping is applied to transform the shape of domain into strip. The image domain extension is proposed to construct symmetry and periodicity for harmonic modeling. The HPB equation is then derived by 2-D convolution theorem and regularized by symmetry analysis. A case study is performed by examining the magnetostatic field distribution of a 6-slot/4-pole permanent magnet machine, and comparing results from finite element analysis validate the HPB model. In light of its accuracy and simplicity, HPB model could be a promising analytical modeling method for electrical machines.