In order to study the curing process of hydroxyl-terminated polyether (HTPE) with different curing agents, aliphatic triisocyanate (N100) and toluene diisocyanate (TDI), the crosslink density (XLD) and chemical processes of the curing reactions have been investigated by low-field NMR spectroscopy and FTIR spectroscopy, respectively, while the mechanical properties of those two cure systems were studied as well. The results show that, for either HTPE/N100 or HTPE/TDI, the higher curing temperature leads to the shorter curing time to reach stability of XLD, while the final XLD decreases by increasing the temperature. The XLD and tensile strength of HTPE/TDI are both lower than those of HTPE/N100, although curing reaction of the HTPE/TDI system is faster and more complete, as seen from FTIR spectra. Besides, the tensile strength of HTPE/N100 based propellant attains the maximum value of 0.64 MPa at NCO/OH ratio of 1.4, while the maximum XLD value of 6.5x 10(-5) mol center dot cm(-3) was obtained at the same time. The XLD is well correlated in tensile strength with the variation of NCO/OH, that suggests regulation of XLD value may be an effective way to optimize the curing conditions for improving mechanical properties of HTPE/isocyanate-based propellants.