With various anti-ship technologies developing in recent years, the survival circumstance of warships is becoming increasingly harsh. Of all, the anti-ship missiles equipped with monopulse seekers have high angular measuring accuracy and strong anti-jamming ability, posing a serious threat to the warships. For the terminal guidance of this kind of missiles, monopulse radar is used to provide angular information of the ship target. Therefore, the research on jamming technologies against monopulse radar has gradually become a research hotspot in Electronic Warfare (EW) field. Cross-Eye Jamming (CEJ) is an Electronic Protection (EP) technique that can yield the wave-front distortion in the worst case, proved to be effective against monopulse radar seekers. Till now, most of the researches on the cross-eye jamming aim at its performance on aircrafts, but few on warships. Given its effect against monopulse radar seekers, cross-eye jamming is taken into account in shipborne Electronic Warfare system. The baseline length of the antennas of the cross-eye jammer is a crucial parameter, which determines whether the anti-ship missiles can be deviated outside the physical extent of the ship. In this paper, the trajectory of interfered missiles is modelled, and the final impact point away from ship is given by the performance analysis of a retrodirective cross-eye jammer, where the platform skin return is considered. Given two typical examples of anti-ship missiles, that supersonic and subsonic respectively, the simulation results present the ranges of valid baseline length for effective ship platform self-protection.