The invention discloses a biomimetic fin unit capable of realizing an elliptical orbit as well as an underwater robot adopting same for propelling. An underwater robot body and biomimetic fin units used in pairs are provided; each biomimetic fin unit comprises a pair of biomimetric fins as well as a driving execution mechanism for driving the pair of biomimetic fin units to realize elliptical orbit water striking and water skiing action; the driving execution mechanism is connected with one pair of biomimetic fins through an output shaft; the driving execution mechanism comprises a biomimeticfin flapping mechanism and a biomimetic fin rotating mechanism; and the flapping mechanism drives the rotating mechanism to generate self-adaptive rotation while realizing elliptical orbit motion. Single motor driven two-degree-of-freedom motion of the mechanism is realized, the biomimetic fins can complete elliptical orbit water striking and water skiing motion within one period, a proper attackangle can be provided, and an ideal angle is achieved within a short time, so that the fin unit has a better flexibility ratio, the propelling property of the biomimetic fin units is improved and themaneuvering property of the underwater robot is improved.