The effects of momentum dependent interaction on the kinetic energy spectrum of the neutron-proton ratiorb(Ek)in the equation of state of nuclear matter was investigated.We found that the kinetic energy spectrum of the neutron-proton ratio rb(Ek) depends sensitively on the momentum dependent interaction and weakly on the in-medium nucleon-nucleon cross section and symmetry potential so that the rb(Ek) is a sensitive physical probe for extracting the information of momentum dependent interaction in the heavy ion collisions. At the same time, the comparing investigate between rb(Ek) for the neutron-rich collision system and the same mass stable collision system gives a important judgment for extracting the information of momentum dependent interaction in the heavy ion collisions.