Fewer studies are addressed about the non-Darcy seepage rule of the offshore heavy oil reservoirs at home and abroad, especially in the aspects of threshold pressure gradient, but the phenomenon is very important for offshore heavy oilfield development, and for in-depth research. According to the percolation characteristics in heavy oil reservoir, a new experimental method for rational determination of the threshold pressure gradient is designed, by which the threshold pressure gradient of heavy oil and flux mobility are deduced using the similar natural cores from QHD32-6 oilfield. The empirical formulas of relations between the threshold pressure gradient and the flow mobility are obtained by regression experimental data. The experimental results indicate that: the threshold pressure gradient is influenced by crude oil viscosity, permeability, and temperature. Through the linear regression above, we can propose the calculation method to determine the technical limit of well spacing and then apply it to the QHD32-6 oilfield. The study above can provide theoretical basis for the offshore development of heavy reservoir.