Abstract：The thermal properties and multi-scale pore structure of different grades and molecular weight nascent ultra-high molecular weight polyethylene (UHMWPE) were investigated by TG, DSC, SEM and 1H spin-spin relaxation. A small molecular solvent cyclohexane was used as a probe to establish a nuclear magnetic relaxation spectrum to characterize the UHMWPE multi-scale pore structure. This method could truly reflect the pore structure and distribution in the nascent UHMWPE. The results showed that the initial decomposition temperature of UHMWPE was 325℃ and the temperature corresponding to the maximum degradation rate was 480℃, which showed its thermal stability. The melting point range of UHMWPE samples was 134~137 ℃, the melting temperature range was 110~150 ℃and the crystallization temperature range was 118~121℃. As the molecular weight increased, the degree of crystallinity of samples decreased. UHMWPE powder was composed of secondary particles with diameter of dozens of micrometers. There were certain gaps among the particles which were connected in a way of fibrous structure. The secondary particles also had a finer internal structure, which basically formed into structures with different pore sizes. The 1H spin-spin relaxation time of cyclohexane in UHMWPE samples was ranged from 0.023 ms to 2 101.750 ms, which basically reflected the macroscopic pore structure and the amorphous pore structure of different scales.