A long period fiber grating is used to detect ethanol concentration of ethanol gasoline and ethanol diesel experimentally.First of all,the long period fib er grating refractive index sensitivity is analyzed by couple-model theory,and the relationship between th e long period fiber grating resonance wavelength shift and environmental refractive index is obtained by the ory.Then it is used to detect ethanol content in ethanol gasoline and ethanol diesel,and at last the re lat ionship between the ethanol concentration of ethanol gasoline and ethanol diesel and long period fiber grati ng resonance wavelength shift is obtained by experiment.The experimental results indicate that as the e thanol concentration change every 1% in ethanol gasoline,the long period fiber grating average reso nance wavelength shift is 0.0477nm,and as the ethanol concentratio n changes every 1% in the ethanol diesel,the long period fiber grating′ average resonance wavelength shift is 1.1544nm.The experimental results we got can fit the theoretical simulation results very well.So the long period fibe r grating could be used to detect ethanol concentration of ethanol gasoline and ethanol diesel.