Abstract: Improvement of passive ranging based on cross spectra leads to an optimized ranging formula applicable to both far and near targets The proposed cross-spectra optimization method is implemented with DSP The system can be used for whole ranging and tracking fast-moving targets In near target ranging,the blind zone of submarine tail ranging is significantly reduced The pro-ranging system can range from 30°to 150°After optimization,the system is capable of ranging from 20°to 160°for targets at 3km and from 10°to 170°for targets at 300m,with errors less than 5% The technique is very useful in improving mobility of submarines.