Cooperative navigation for multi-UUV is localizing all members of a team of UUVs by proprioceptive and exteroceptive sensors through acoustic link among UUVs. In the Leader-Fellow structure, the master UUV is equipped with high accuracy sensors, the slave UUV is equipped with low precision sensors added with underwater sonar which provide relative observations between UUVs. The slaver gets the position information from the master by the acoustic modem. The mode of underwater communication for multi-UUV is presented based on acoustic signal one-way-travel-time (Time-Of-Flight, TOF). Proprioceptive and exteroceptive data are fused with an Extended Kalman Filter, the equations are derived for this estimator for relative distance and bearing between two UUVs. Finally, the performance of the approach through a simulation based on Matlab is studied, the research results prove that the navigation accuracy has been improved effectively by using this cooperative navigation method.