In this paper, the evolution of mechanical properties and capillary water absorption properties of sulfoaluminate cement (SAC) mortar with different water-cement ratios (W/C) with age was investigated. The pore structure of SAC mortar at specific age and dynamic pore structure during the hardening process were characterized based on low field nuclear magnetic resonance (LF-NMR), combined with mercury intrusion method, water absorption data and theoretical model, the value of the surface relaxation rate of SAC mortar was discussed. The results show that after 0.5 d of standard curing, the compressive strength and flexural strength of SAC mortar with W/C of 0.45, 0.50 and 0.55 are 23.5, 20.8, 16.2 and 4.2, 3.9, 3.6 MPa, respectively, which can basically reach more than 60% of those at 28 d age. At the age of 0.5 d, the capillary water absorption coefficients of SAC mortars with different W/C are 0.020~0.042 g·cm-2·min-0.5. At age of 3 d, the capillary water absorption coefficients decrease by 18.5%~25.0%. Thereafter, it changed little until age of 28 d. Within 0.5 d after adding water and mixing, the pore structure of SAC mortar evolves rapidly, and the porosity and pore size distribution gradually stabilize during 0.5~3 d age. The representative capillary tube diameters deduced from data such as capillary water absorption coefficients and theoretical models are closely related to the pore diameters of SAC mortar based on LF-NMR T2 spectra. When the values of the surface relaxation rate in the fast exchange model are in the range of 0.005 5~0.042 0 μm/ms, the two are relatively close.