In this study, the low-field nuclear magnetic resonance (NMR) testing technique was adopted to experimentally investigate the seepage processes of chemical grout flow in fractured rock mass under various confining pressures and temperatures. The variations in the NMR parameters, including the tested porosity, transverse relaxation time (T2) distribution and T2 peak area were quantitatively analyzed to study the seepage characteristics under different grouting conditions. The changes in the grout viscosity against the temperatures were studied. Then the effects of injection pressures and temperatures on the seepage characteristics of the porous sandstone with a single fracture under constant confining pressure of 20 MPa were systematically investigated. The results indicate that the viscosity of the grout shows obvious time-dependency characteristics and is strongly affected by the temperatures. The flow pattern of the grout is greatly dependent to the injection pressure, whereas it is less affected by the temperature. The permeability of the porous sandstone shows an increase trend as the injection pressure increases and the temperature decreases.