Difference of physical property of each stratum can cause different advancing velocity of water-oil frontal edge during the waterflooding stage in ultra-low permeability multilayer reservoir. Using seepage theory of ultra-low permeability multilayer reservoir,considering threshold pressure gradient for oil and water, a theoretical model is established and the formula of water-oil frontal edge is deduced. In addition, the influence of permeability differential, injection-production differential pressure, injection-production well spacing and oil viscosity on the water-oil frontal edge is also analyzed. Considering the influence of injection-production well spacing,the dimensionless water-oil frontal edge is first proposed. The result shows that: The greater the permeability differential, the slower the advancing velocity of water-oil frontal edge for the lower stratum; with the increase of the injection-production differential pressure, the advancing velocity of water-oil frontal edge for the lower stratum is becoming faster, but the amplitude increment is becoming smaller; with the increase of the injection-production well spacing, the distance of water-oil frontal edge for the lower stratum is becoming longer, but the dimensionless water-oil frontal edge is becoming smaller; with the decrease of oil viscosity, the advancing velocity of water-oil frontal edge for the lower stratum is becoming faster, and the amplitude increment is becoming larger.