Polyamide-imide-based film, preparation method thereof, and cover window and display device comprising the same

A polyamide-imide-based film, which has a content of nitrogen (N) elements in the film of 6 to 7.5% by weight based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film,

• wherein when the transmittance, haze, yellow index, and modulus are each measured at six points in total, in which two arbitrary points are selected in each of region N, region C, and region S partitioned in the TD direction of the film,
• the average value of transmittance is 80% or more, and the deviation rate of transmittance is 0.3% or less,
• the average value of haze is 1% or less, and the deviation rate of haze is 10% or less,
• the average value of yellow index is 5% or less, and the deviation rate of yellow index is 10% or less, and
• the average value of modulus is 5 GPa or more, and the deviation rate of modulus is 10% or less.