Underwater　robots　are　critical　observation　platforms　for　diverse　ocean　environments.　However,　existing　robotic　designs　often　lack　long-range　and　deep-sea　observation　capabilities　and　overlook　the　effects　of　environmental　uncertainties　on　robotic　operations.　This　article　presents　a　novel　long-range　underwater　robot　for　extreme　ocean　environments,　featuring　a　low-power　dual-circuit　buoyancy　adjustment　system,　an　efficient　mass-based　attitude　adjustment　system,　flying　wings,　and　an　open　sensor　cabin.　After　that,　an　extended　environment　perception　strategy　with　incremental　updating　is　proposed　to　understand　and　predict　full　hydrological　dynamics　based　on　sparse　observations.　On　this　basis,　a　real-time　dynamic　modeling　approach　integrates　multibody　dynamics,　perceived　hydrological　dynamics,　and　environment-robot　interactions　to　provide　accurate　dynamics　predictions　and　enhance　motion　efficiency.　Extensive　simulations　and　field　experiments　covering　600　km　validated　the　reliability　and　autonomy　of　the　robot　in　long-range　ocean　observations,　highlighting　the　accuracy　of　the　extended　perception　and　real-time　dynamics　modeling　methods.　　©　2025　IEEE.