  Flood front is the jump interface where fluids distribute discontinuously,
whose interface condition is the theoretical basis of a mathematical model of
the multiphase flow in porous medium. The conventional interface condition at
the jump interface is expressed as the continuous Darcy velocity and fluid
pressure (named CVCM ). Our study has inspected this conclusions. First, it is
revealed that the principle of mass conservation has no direct relation to the
velocity conservation, and the former is not the true foundation of the later,
because the former only reflects the kinetic characteristic of the fluid
particles at one position(the interface), but not the neighborhood of the
interface which required by the later. Then the reasonableness of CVCM is
queried from the following three aspects:(1)Using Mukat's two phase seepage
equation and the mathematical method of apagoge, we have disproved the
continuity of each fluid velocity;(2)Since the analytical solution of the
equation of Buckley-Leveret equations is acquirable, its velocity jumps at the
flood front presents an appropriate example to disprove the CVCM;(3) The
numerical simulation model gives impractical result that flood front would stop
moving if CVCM were used to calculate the velocities at the interface between
two gridcells. Subsequently, a new one, termed as Jump Velocity Condition Model
(JVCM), is deduced from Muskat's two phase seepage equations and Darcy's law
without taking account of the capillary force and compressibility of rocks and
fluids. Finally, several cases are presented. And the comparisons of the
velocity, pressure difference and the front position, which are given by JVCM,
CVCM and SPU, have shown that the result of JVCM is the closest to the exact
solution.
