The invention relates to a device and a method for detecting unrecognizable leakage in containment. The device comprises a meter support, a liquid level sensor and a transmitter, wherein the liquid level sensor is arranged in a pit; the transmitter is used for transmitting detection data; a digital instrument control system is used for generating unrecognizable leakage information and an alarm command. The method comprises the following steps: (1) acquiring liquid level detection data; (2) generating liquid level variation data according to the liquid level detection data, and generating the unrecognizable leakage information; (3a) displaying the unrecognizable leakage information; (3b) analyzing, processing, and generating the alarm command; (4) executing an alarm action according to thealarm command. The device and the method have the beneficial effects that the intelligent liquid level transmitter is used for replacing a pressure transmitter and a liquid level switch, so that the instrument model selection is simplified, the manufacturing cost is reduced, the construction difficulties such as insufficient installation are avoided, and the inherent defects that the remote pressure transmitter and the mechanical liquid level switch are large in error, high in requirements for installation, prone to failure, and difficult in adjustment are overcome.