The polarization-dependent loss (PDL) of long-period fiber gratings (LPFGs) etched by high-frequency CO2 laser pulses through single-side and dual-side exposure technologies was investigated. Long-period fiber gratings induced by the single-side exposure method depend greatly on the polarization state of incident light and have large polarization-dependent loss due to the asymmetry of refractive index profile in its cross section. A new dual-side exposure method is applied in long-period fiber gratings writing process to reduce polarization-dependent loss by uniforming the refractive index profile in the fiber cross section. Experimental results show that polarization-dependent loss of the long-period fiber gratings drops down to 0.42 dB by using dual-side exposure technology compared with 1.24 dB by the single-side exposure method. The dual-side exposure technique overcomes the influence of polarization state of incident light and can produce low-polarization-dependent loss long-period fiber gratings which can be widely used in optical fiber communication and sensing systems.