To replace the existing manual method for measuring the ethanol content in petrol stations and improve the detection efficiency of oil quality at the station end, a new method for the on-site real-time detection of the ethanol content in ethanol gasoline is proposed. The proposed method is based on the refractive index sensitivity of the tilted fiber Bragg grating (TFBG) and can reflect changes in the refractive index of ethanol gasoline attributed to different ethanol contents. The spectral characteristics of the TFBG are analyzed using the couple model theory, and the sensing characteristics of the TFBG for ethanol content detection in ethanol gasoline are investigated. Experimental results show that in the detection of ethanol gasoline with ethanol contents of 8.3%-14.3%, the proposed method achieves a sensitivity of 6.5 nm/RIU (RIU refers to the refractive index unit) and a linear fitting degree of 0.949. The detection accuracy of the E10 ethanol gasoline sample is verified using the wavelength demodulation method, yielding a detection value of the ethanol volume fraction of 10.2% and a relative error of 2%. These findings verify the feasibility of TFBG for ethanol content detection in ethanol gasoline.