Abstract: Quenching and bromination were applied to the pretreatment of LLDPE samples to eliminate the interferences due to crystal field and terminal -C=C- group in the carbon chain in FTIR spectrometry.As shown by the result of this modification,(1) strong and sharp symmetrical transform vibration spectral band of methyl group δs(CH3) at 1 378 cm-1 was obtained and separated clearly from the external-facing swinging vibration spectral band of methylene group at 1 368 cm-1,indicating the existence of only one single branch chain in the molecular chain;(2) internal-facing swinging vibration spectral band near 890 cm-1,characterizing the presence of long branch chain,was not observed,and only the internal-facing swinging vibration spectral band of methylene group at 772 cm-1 was found,indicating the existence of ethyl branch chain.The proposed method was used successfully as a rapid and simple method for the identification of LLDPE with 1-butene as monomer in the copolymerization.It also gave an important idea for the identification of LLDPE with other α-olefin as monomer.