One of key technologies for torpedo guidance simulation is refined modeling of multi-target echo synthesis under the complex underwater acoustic environment. The complex underwater acoustic environment concept and basic point target echo model were introduced, and the multi-target echo synthesis method has been studied comprehensively under the conditions of different combination of far-field and near-field, point target and body target. The mathematical model is established, and the simulation results under typical conditions are given. The multi-target echo synthesis could be as reference of torpedo guidance simulation under the complex underwater acoustic environment.