Since the disadvantages and limitation of anti-collision system with radar in aircraft ( ACSR-anti-collision system with radar
in aircraft) ，the terrain avoidance strategy was proposed，which adopted the virtual radar to substitute the airborne radar system to solve
the problem of the terrain anti-collision． According to characteristics of aircraft motion，uniform motion model，uniformly accelerated
motion model and the current statistic model were established，which are suitable for fast and accurate prediction． The principle of the
interacting multiple model and Kalman filtering were adopted to predict the aircraft flight conditions in real time which were used to
match the airborne terrain database to avoid crash． The prediction arithmetic was testified by simulation，and the results show that the
prediction time has important effect on deviation． But the warning level can be determined according to the forecast time． The research
demonstrated that terrain avoidance is much more advanced than ACSR，and it can replace ACSR．