In this paper, a set of microwire arrays based on Ni-Fe/Cu composite wires were fabricated as the multicore sensing elements with different number of wires and different structures. The longitudinal hysteresis loops showed that the anisotropy of the arrays changed in different structures. The sensitivity of the multicore orthogonal fluxgate sensor increased exponentially with the increase of number of wires in the arrays, whereas the noise level depended on the working mode and structure of the microwire arrays. In the fundamental mode, a minimum noise level of 42 pT/rtHz@1 Hz was obtained with a 5-wire array, and in the second harmonic mode a minimum noise level of 177 pT/rtHz@1 Hz was obtained with the same array. Investigation of the relationship between the magnetic properties and the microwire array structures revealed a collective compactedness value which is able to describe the interaction effect in wires and to predict the favorable array structure based on the ratio of effective contact volume to the total material volume.