Numerical methods can handle any geometrical configuration, time-depending problems and both linear and non-linear cases. Two 3D FEM models were developed in the Russian Cable Institute to optimize both coaxial and triaxial 2G HTS cables. In addition, with the help of the 3D FEM model, we can calculate the hysteresis losses in a NiW substrate of 2G HTS tapes of the cable. The transient 2D FEM model was developed and used for calculation of AC losses in the cables and stacks of 2G HTS tapes. For the correct calculation of the AC losses, it is important to determine the parameters in an empirical expression describing critical current density of the 2G HTS tapes dependence from the vector magnetic field and its non-uniformity across the tape width. In this work, the described above FEM models are briefly presented.