According to the procedure of on-call submarine search with passive sonobuoy arrays,the deployment radius was explored by using probability theory and optimal search theory.When using sonobuoy array for on-call submarine search,the distribution characteristics of the initial position,speed and course of the submarine was studied,the analytic model of search probability was obtained,and the deployment radius that has the maximum submarine search probability,called improved deployment radius,was derived based on the model.The submarine searching model of anti-submarine helicopter using typical dropped sonobuoy array was established,and the submarine search efficiency was analyzed with Monte Carlo simulation according to the model.The simulation results show that: 1) The search probability obtained by computation with the analytic model is basically identical to that of the Monte Carlo simulation; and 2) Compared with the sonobuoy array using conventional deployment radius,the sonobuoy array with the improved deployment radius has higher search probability and requires less quantity of sonobuoys.