Fiber-based piezoelectric composites offer the advantages of excellent flexibility and geometric scalability in the applications of bio-inspired locomotion and flexible actuation. A biomimetic underwater propeller mimicking the body or caudal fin (BCF) oscillating behavior of carangidae fish is proposed, and macro fiber composites (MFC) are used as actuators. Oscillation performance of the propeller is presented at different actuation voltage levels. Experimental results show that the maximum oscillating displacement of the proposed propeller in air is 45 mm (peak-to-peak value), with the actuation of 1 000 V (peak-to-peak value) at 17.7 Hz. The distributions of flow field and vortexes around the propeller tip in a steady oscillating cycle are obtained by the use of computational fluid dynamics (CFD) technologies. The anti-Karman vortex street phenomenon is revealed during the time sequence of vortices generation, expand, shed and breakdown processes. Meanwhile, a jet flow ejecting downstream the tip between the two counter-rotating vortices is observed. Accordingly, the propulsion locomotion of the propeller is achieved with the reactive force of the jet flow. Thus, the propulsion mechanism of the proposed biomimetic underwater propeller is demonstrated. The average propulsion force at the end of the propeller in the x direction is up to 1.5 mN.