A dual-peak resonance long-period fiber grating (LPFG) based on CO₂ laser technology is proposed to investigate a highly sensitive refractive index sensor. First, dual-peak resonance LPFGs with grating periods of 196 and 73 μm are fabricated in conventional single-mode fiber and 80 μm bend-insensitive single-mode fiber, respectively,using a CO₂ laser after etching cladding. This demonstrates the possibility of fabricating an LPFG on a single-mode fiber with a shorter grating period using CO₂ laser micromachining technology. Dual-peak resonance LPFGs with grating periods of 110 and 115 μm are directly fabricated in two 80 μm single-mode fibers using a CO₂ laser. The results show that the dual-peak resonance LPFGs fabricated in two 80 μm thin single-mode fibers exhibit advantages of deep attenuation loss, low loss, and high refractive index sensitivity. Based on its excellent performance, the dual-peak resonance LPFG based on CO₂ laser technology is a prospective sensor applicable to fields such as biological, chemical, and environmental parameter detection. In addition, a simple-operation low-cost method for fabricating dual-peak resonance LPFGs is proposed.