The ship borne missile is affected by the ship attitude and velocity during launch， which changes its attitude， position and velocity. Under the background of high sea conditions， in order to avoid the mutual interference between two missiles launched at intervals， the safety area of initial trajectory after launch is studied. According to the motion characteristics of vertical launch missile in the initial flight phase， the ballistic launch safety area model is established； the ballistic safety zone of two missiles at different launch times is defined. The model solves the problem of defining the launch safety area of high sea situation missile， and has practical engineering application value.