The invention discloses a tail fin included angle changing mechanism with a cruising mode and a charging mode capable of being interchanged. The tail fin included angle changing mechanism with the cruising mode and the charging mode capable of being interchanged is composed of a shell, an electromagnetic switch, a pin, a variable ratchet mechanism, a rack, a gear, a shaft, a tail fin and a spring. The gear and the tail fin are symmetrical about the rack. When a bionic robotic fish needs to be in a cruising (charging) state, the electromagnetic switch is powered on, a movable iron core of the electromagnetic switch drives a left ratchet to move rightwards, the toothed right end of the left ratchet makes contact with a right ratchet and then drives a positioning block on the right ratchet to get away from a positioning groove (sliding groove), and the right ratchet is forced to rotate. After the electromagnetic switch is powered off, the movable iron core drives the left ratchet to move leftwards to reach the initial position, the positioning block of the right ratchet moves leftwards under the action of the spring and is locked at the left end of the sliding groove (positioning groove), and therefore the rack is driven to move leftwards (rightwards), and the rack moves to drive the gear to rotate so that the tail fin can incline backwards relative to a fish body and the cruising (charging) state can be achieved. By means of the tail fin included angle changing mechanism with the cruising mode and the charging mode capable of being interchanged, the cruising capacity of the robotic fish is improved, and work quality of the robotic fish is guaranteed.