Solid-state magnetic sensors can be arranged around multi-conductors to measure currents by sensing the field in a non-contact way. To improve the accuracy of measurement， the basic principles for the topology design of sensor arrays must be studied. To study the theoretical measurement errors caused by sensors array arrangements， a topology optimization model based on discrete Fourier transform（DFT） for sensor arrays is presented. The model aims to minimize the condition number of coefficient matrix which associates the sensors outputs and the measured currents， and several constraint conditions are listed as well. The model can be used both for AC and DC current measurements. Moreover， it has no restriction on the number of parallel conductors. An application on a three-phase current system is presented in details， and the results validate the effectiveness of the proposed method.