Abstract: When rocket-assisted torpedo is adopted to attack submarine,the over-the-horizon fire channel taking helicopter-dipped sonar as information instructing resource can take advantages of long range and high speed of rocket-assisted torpedo completely.The precision of target motion factor and the channel reaction time determined by the fire channel have significant influence on fire channal performance.In this paper,the precision of target motion factor and the channel reaction time are analyzed, and the formulas are deduced.Simulation is performed with Monte-Carlo method to analyze their effects on fire efficiency of rocket-assisted torpedo.Moreover,some methods for improving the precision of target motion factor and the channel reaction time are suggested.