The optical response of an inverted InAs/GaSb quantum well is studied theoretically.The influence of an in-plane magnetic field that is applied parallel to the quantum well is considered.This in-plane magnetic field will induce a dynamical polarization even when the electric field component of the exteal optical field is parallel to the quantum well.The electron-electron interaction in the quantum well system will lead to the de-polarization effect.This effect is found to be important and is taken into account in the calculation of the optical response.It is found that the main feature in the frequency dependence of the velocity-velocity correlation function remains when the velocity considered is parallel to the in-plane magnetic field.When the direction of the velocity is perpendicular to the in-plane magnetic field,the depolarization effect will suppress the oscillatory behavior in the corresponding velocity-velocity correlation function.The in-plane magnetic field can change the band structure of the quantum well drastically from a gapped semiconductor to a no-gapped semi-metal,but it is found that the distribution of the velocity matrix elements or the optical transition matrix elements in the wave vector space has the same two-tadpole topology.