This paper first summarizes a general optical communication model for underwater nodes and takes node survival rate as the reliability index of cabled seabed observatory networks.In view of reduced reliability and increased difficulty in cable installation arising from multiple underwater branching nodes

it optimizes NEPTUNE into a crossed ring topology that contains only two multi-branching nodes.The reliability simulation results of the above two kinds of networks reveal that the crossed ring topology is similar to NEPTUNE in reliablity

but more favorable for power supply and network installation because of less number of branching nodes.