In order to provide a decision making support for commander formulating searching submarine plan, this thesis established a detection probability model of antisubmarine helicopter linear roundtrip patrol in searching submarine by using dipping sonar. Proposed different search schemes by using two antisubmarine helicopters and calculated the detection probability based on three typical schemes, then the paper gave the optimal suggestion. The research results indicates that this method provides a useful theoretical basis to formulating searching submarine plan and the method can also be popularized in making searching plan of many antisubmarine helicopters linear patrol in searching submarine by using dipping sonar.