Polyester film and preparation method thereof

The polyester film according to the present embodiment includes a polyester resin. The polyester resin includes a repeating unit having a cyclohexane skeleton and a repeating unit having a benzene ring. The polyester film is formed by using a Fourier transform infrared spectroscopy (Fourier transform infrared spectroscopy), and then using the Fourier transform infrared spectroscopy (Fourier transform infrared spectroscopy). A spectrum measured by FT-IR) has a reference peak which is a peak related to bending vibration of the benzene ring and a first peak which is a peak related to C-O stretching vibration. The reference peak is a peak at a wave number of 788 cm to 798 cm . The first peak is a peak at a wave number of 1129 cm to 1139 cm . The intensity difference between the reference peak and the first peak is-0.05 to + 0.05. The present embodiment can impart excellent heat resistance, mechanical properties, and the like to a film by applying a polyester resin having a controlled degree