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Existing miniature underwater robots, which use electromagnetic actuators or soft actuators, function in shallow waters. However, in the deep sea, the robots face challenges, such as the miniaturization of the pressure protection unit and the driving method for rapid and agile motions. Herein, a jet‐driven method for a high‐pressure underwater environment is proposed by utilizing the high‐frequency vibration of a piezoelectric vibrator. Thereafter, an antihydropressure miniature robot with a body length of less than 5 cm is designed, which can perform the highly agile actions of floating, sinking, hovering, straight driving, and turning under a water pressure of 20 MPa (equal to the pressure under a water depth of 2000 m). A vertical velocity of 2.95 BH/s and a horizontal velocity of 3.22 BL/s are realized by the prototype, and it achieves faster motions than existing miniature underwater robots. Some potential applications have been realized, including small multicorner pipe exploration by carrying a camera, seaweed epidermal cell sampling in designated areas, and large object transportation by swarming, which proves the high maneuverability and agility of the developed robot. These merits make the robot ideal for multitasking operations in narrow environments with high water pressure, such as multiobstacle seabed.

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The valveless piezoelectric micropump has the advantages of simple structure, high precision and low cost, which can realize the directional transport of micro-fluid and wildly be applied in a micro analysis system. However, backflow at the outlet cannot be avoided due to the limitation of its working mechanism. Large reflux rate can increase the volume control accuracy per cycle, but reduces the stability of the micro analysis system. In order to achieve a full forward flow, which reduce the influence of backflow on the system’s stability, the reflux characteristics of the designed valveless piezoelectric micropump were studied. The condition proposed, which should be satisfied for obtaining full forward flow, is that the reflux rate should be less than 50%. The influence of relations between the size of the key structures and pumping characteristics are established, and the references for structural parameter selection to reduce backflow and achieve full forward flow are given. This paper highlights the methods of controlling the pumping performance and achieving full forward flow, based on structural parameter selection analysis and adjusting excitation. The reflux rate can be reduced to 5% when the inlet angle is increased to 9°. The experimental results verify the validity of the obtained results and the proposed methods of control. This work provides important references for applying valveless piezoelectric micropumps in micro analysis and precision-driven systems.