Relative permeability was an important basic measurement parameter in heavy oil development experiment. Due to the high viscosity of heavy oil, oil-water emulsification was prone to occur during water flooding process, which made it difficult to obtain the heavy oil-water relative permeability curve accurately. The traditional measurement method of relative permeability curve regarded the core as a "black box", and measured the volume of oil and water at the outlet by the method of manual reading or weighing, which had the disadvantages of low measurement accuracy and less information. In order to accurately measure the heavy oil-water relative permeability curve, this paper selected the long artificial sandstone core. Based on the nuclear magnetic resonance measurement technology, through the simultaneous calibration of crude oil and formation water of Bohai B reservoir, the unsteady state method was used to measure the heavy oil-water relative permeability curve, and the T2 spectrum test was carried out on the core and the produced fluid at the outlet. Thus, the pore volume (147.18cm³), irreducible water saturation (25.9%), residual oil saturation (43.83%) of the core and the oil and water content at the outlet were obtained more accurately, and the heavy oil-water relative permeability curve was obtained more accurately. Moreover, the D/T2 two-dimensional spectrum test was carried out on the produced fluid with oil-water emulsification, and the emulsification of oil and water was judged more accurately. The research results can provide some theoretical guidance for the development of heavy oil water flooding, which is beneficial to the study of the mechanism of heavy oil water flooding.