The dacron crystal structures (ν-crystal-dacron) were studied by infrared (IR) spectrum, for instance, ν-crystal-1-dacron(1335 cm.1), ν-crystal-2-dacron(969 cm.1), and ν-crystal-3- dacron(847 cm.1). In addition, the dacron thermostability was studied by temperature-dependent infrared(TD-IR) spectrum. We obtained that the corresponding absorption intensity and frequency of dacron ν-crystal-dacron were changed (353-393 K) because its crystal structure was destroyed by the temperature. We further studied the glass transition of dacron ν-crystal-dacron was by two- dimensional infrared(2D-IR) spectrum. During heating, the dacron macromolecular chain showed different motion states. The dacron molecules froze in molecular motion before the glass transition temperature (313-343 K); however, these molecules nearly entered a high elastic state after the glass transition temperature (353-393 K). This study demonstrated the key roles of three-step infrared spectrum (including IR spectrum, TD-IR spectrum, and 2D-IR spectrum) in the analysis of structure, thermostability, and glass transition of the important polymer material(dacron).