With the development of the technology for defence against anti-ship missile, anti-ship missile is facing a new challenge. Therefore, the technologies of stealth, variable trajectory, electronic countermeasure and supersonic flight must be used to improve the penetration efficiency and strike effect, in which the variable trajectory and supersonic flight technologies are all affected by the propulsion equipment. The different variable trajectory methods are described. The ramjet constraint is analyzed. The influence of different parameters on the performance of anti-ship missile and some limiting factors to the propulsion device are discussed.