The typical manner to generate the axial magnetic force is to utilize the magnetic path design by upward magnet offset (UMO) that is the permanent magnet (PM) shifted upward relative to the stator in the single-phase BLDC slim fan motors. The other special method is to increase a permeable material, with an air-gap (AGi-m), under the PM to generate the axial magnetic force. The axial magnetic force and its ripples are the important factors in the slim fan design and will further affect the performances of the acoustic noise and axial vibration. In this project, a magnetic circuit model is constructed to execute the mathematical theoretical analysis of the magnetic field. The trait of the phase opposition between the magnetic force ripples generated in the stator core and lower iron plate is used to optimize the ripple of the total axial magnetic force by the offset effect, and in the meantime, to remain the desirous average value. A three-dimensional (3-D) model is created to execute the finite element analysis and simulation. The cross-matching simulation among the different degrees of UMO and AGi-m is executed and an optimized model is defined. A solid model of a slim fan motor is verified in the practical experiment and the results present the effectiveness in the reduction of the acoustic noise and vibration.