Relative permeability is an important basic measurement parameter in heavy oil development experiment. Due to the high viscosity of heavy oil，oil-water emulsification is easy to occur during water flooding，which makes it difficult to obtain the heavy oil-water relative permeability curve accurately. The traditional measurement method of relative permeability curve has the disadvantages of low measurement accuracy and less information. In order to accurately measure the heavy oil-water relative permeability curve，the artificial sandstone long core was selected，the heavy oil and formation water of Bohai B reservoir were calibrated at the same time based on low field nuclear magnetic resonance measurement technology. The unsteady state method was used to measure the heavy oil-water relative permeability curve. The results showed that the pore volume（147.18 cm³），bound water saturation（25.9%），residual oil saturation（43.83%）and oil and water content at the outlet of core were accurately obtained by T₂ spectrum test of the produced liquid in the core and at the outlet，meanwhile the heavy oil-water relative permeability curve was obtained more accurately. Through the D/T₂ two-dimensional spectrum test of the produced liquid with oil-water emulsification， it could be more accurate to judge whether the oil-water emulsification occurred. The research results could provide some theoretical guidance for the heavy oil development by water flooding，which was beneficial to the exploitation mechanism study of heavy oil by water flooding.