Due to its compact construction and high power density, the axial-flux permanent-magnet (AFPM) machine with coreless stator has obtained more and more attention and interest from researchers. For an AFPM machine with coreless stator, the axial magnetic attraction force may cause the rotors’ deflection and affect the machine’s reliability. In this paper, the magnetic field and the rotor mechanical strength of a coreless stator AFPM machine are studied. Finite-element method and analytic method are both used to calculate the axial attraction magnetic force between the two rotor discs. Structure finite-element analysis is used to simulate the maximum stress and deflection due to the axial magnetic force. The research is very significant to the power density elevation of the AFPM machine.