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• Fastener stiffness increases with service time in high-speed railway. • Fastener stiffness is sensitive to low temperature and high frequency. • The temperature- and frequency-dependent characteristics of fastener affect rail vibration and decay rate. • PUEP composed of PTMG1000 and NDI has wide temperature range stiffness characteristics. The operation line of China's high-speed railway has exceeded 40,000 km. The performance decay and even failure to some fastener systems could be caused by complex terrain (mountain and plain), variable environment (−50 °C to 50 °C), high speed (300–350 km/h) and high frequency (500–700 Hz). Herein, the W300-1 fastener is taken as the research object to test and conclude the service performance and online track modal recognition. The comprehensive test system is used to obtain the dynamic characteristics of fasteners with the preload under the temperature-dependent (−70 °C to 50 °C) and frequency-dependent (10–1250 Hz) coupling conditions. It is found that the elastic pad stiffness in fastener system is sensitive to the low temperature and high frequency. In order to study the influences of temperature- and frequency-dependent dynamic characteristics of fasteners on track system, the dynamics analysis model of track system is constructed. The rail receptance curve under constant working condition is verified by the online track recognition. Simultaneously, the dynamic characteristics of the rail under constant working condition (4 Hz) and temperature-/frequency-dependent conditions are contrastively analyzed. The results indicate that the frequency-dependent characteristics of elastic pad enable the first-order modal frequency to shift toward a higher frequency, accompanied by the amplitude increase. The temperature-dependent characteristics of elastic pad make the medium- and high-frequency decay rate of rail wider but smaller. Due to the adverse effects of above conclusions, the polymer materials of elastic pad in fastener system are modified and optimized from two perspectives of polyol type and crosslinking agent type. Based on the standard requirements of Q/CR7-2014, it is certain that the dynamic performances of PUEP samples prepared by PTMG1000 and NDI together can meet the requirements of safety and stability of high-speed railway. [ABSTRACT FROM AUTHOR]