Based on the optical model of D type of side-polished photonic crystal fiber (SPPCF), both the attenuation of optical power and the field distribution of propagation modes in the device of SPPCF are calculated and analyzed with the variation of geometry factors, such as residual radius after side polishing, axial rotation angle, and the length of side-polished area, by using three-dimensional finite difference beam propagation method (FDBPM). The analysis results show that when the residual radius is longer than -1.5 μm, the shorter the residual radius is, the larger the attenuation of the optical power in SPPCF is; the optical power of LP01 mode of the SPPCF is attenuated in the side-polished area, and recovered after light passes through the side-polished area. When the residual radius is longer than 0.5 μm, there is a small difference between the attenuations of optical power of PCFs polished at different axial rotation angles. When the residual radius is small enough, high order modes appear during the process of the light passing through the side-polished area. The mode field distribution is the most dispersive one and many high order modes appear in side polished area when the axial rotation angle is 30°. When the residual radius is longer than 1.5 μm, the change of the side-polished length has a little impact on the attenuation of optical power in SPPCF; when the residual radius is shorter than 1.5 μm, the attenuation of optical power changes in oscillation as the side-polished length varies. The analysis may provide a theoretic guide to device fabrication of SPPCF.