Plastic film is a bulk type accounting for one-fifth of plastic products in China. One of the most important indicators in manufacturers production is the thickness of plastic film. How to accurately, quickly and conveniently measure the thickness of plastic film is a research topic with great economic value. In this paper, in order to verify the feasibility of measuring the thickness of the plastic film by X-ray absorption spectroscopy, experimental samples of polyethylene plastic film with different thicknesses are made, and the 30 kV pipe voltage and 1 μA. The tube current of A excites X-rays, irradiates plastic film samples of different thicknesses, collects blank spectral data and original X-ray absorption spectral data of different samples with X-ray detector, and obtains photon intensity of each spectrum in 256 channels. In the process of data analysis, in order to achieve the effect of data dimension reduction, principal component analysis is selected to process the collected data; The new dataset with reduced dimension is analyzed two times, one for machine learning directly and the other for machine learning after normalization. In machine learning, 70% are used as training sets, and the remaining 30% are used as test sets. The input data is the X-ray absorption spectra of each group of samples, and the output data is the plastic film thickness predicted by the model. At the same time, to reduce the error caused by randomness, multiple trainings were conducted to evaluate the effect of thickness estimation with average accuracy. Finally, comparative analysis of experimental data concludes that when the error tolerance is set to 50 μm, the accuracy of measuring the thickness of the plastic film by using the machine-learned X-ray absorption spectroscopy after normalization can reach 98.4%. At the same time, as long as the number of samples of the original spectral data is increased and the sampling distribution of different thicknesses is effectively planned, the accuracy of this method can be greatly improved in theory and can be extended to the thickness measurement task of other materials. Compared with other thickness measurement methods on the market, X-ray absorption spectroscopy has the advantages of nondestructive testing, rapid testing and a wide application range, which has a good application prospect for enriching the plastic film thickness measurement technology of manufacturers production lines and relevant regulatory departments, improving the thickness measurement efficiency and improving the measurement accuracy. It has a good application prospect to enrich the thickness measuring technology of plastic film of the production line and related supervision department, improve the thickness measuring efficiency and accuracy.