According to the coupled-mode theory,the spectral and coupling characteristics of the double-helix chiral long period fiber grating(CLPGs) were analyzed.Using the phase matching conditions,the rotational period and torsion ratio corresponding to the specific resonant wavelengths were calculated.The relevant transmission spectra were simulated and the influence of the design parameters of gratings on the transmission spectrum was discussed.Finally,the strain sensing features of the double-helix CLPGs were analyzed.The research results show that the sensing properties of this grating are similar to that of the traditional long-period fiber gratings,which means the resonance wavelength will shift with the change of the strain,moreover,the wavelength shift is almost linearly with the strain,and the strain sensitivity is 0.828 pm/με.