Abstract: During the process of acquiring 3-D seismic data, there wil be platform, reef or small island in the work area sometimes.Undershooting is a good way to acquire the data of that obsta cle. By principle of acquiring 3-D seismic data, it is acceptabl to get enough data of underground in the explore surface if th
data with enough coverage and the gridnet of geophone is satified the 3-D sampling principle. The principle of undershootin and the configurations of source and navigation system and in stallation of near field hydrophone of source vessel have been explained. In practice, source vessel with this way has gotten excellent effect.

Key words: undershooting, source vessel, configuration, source