The disclosure provides a pressure sensing device used for tunnel secondary-lining thickness monitoring and a use method. The pressure sensing device used for tunnel secondary-lining thickness monitoring includes a fixing portion and a pressure monitoring portion. The fixing portion is used for fixing in a structural opening. The structural opening is formed by inward digging of a primary-lining surface. The pressure monitoring portion includes an air pressure tube. One end of the air pressure tube is connected with the fixing portion in a sealing manner, and the other end is connected with amoving portion in a sealing manner. The moving portion is also connected with a floating label. A pressure sensor is disposed in the air pressure tube, and is connected with a monitor, and is used formonitoring pressure in the air pressure tube in real time, and the thickness of a secondary lining of a tunnel reaches a preset requirement when the thickness of the secondary lining is in contact with the floating label and the pressure in the air pressure tube has a change.