In this article, the parallel-hybrid-excited harmonic-shift machine (PHE-HSM) is analyzed from the perspective of the field-modulation effect based on the air-gap field harmonics. By shifting the pole-pairs of the dc-field windings from those of the permanent magnets (PMs), the parallel-hybrid excitation can be realized due to field modulation. The operation principle and the torque production mechanism of the PHE-HSM are elaborated from the perspective of the field-modulation effect. Moreover, it is revealed that the effective harmonics are those with even pole-pairs, while the dominant harmonics are those with pole-pairs of $\vert kN_{\mathrm{ r}} \pm (4 i - 2) p_{\mathrm{ s}}\vert $ ( $k = 1, i = 1, 2, 3$ ) and ( $4i-2$ ) $p_{\mathrm{ s}} (i = 1, 2, 3)$ . By regulating the even harmonics, the flux linkage, back electromotive force, and torque can be enhanced and weakened accordingly. The prototype is also constructed to experimentally verify the analysis and simulation.