An extrinsic optical fiber Fabry-Perot acoustic emission sensor and an ultrasonic detection device comprising the same relate to the field of optical fiber sensing technology. The problem that a conventional diaphragm-coupling extrinsic Fabry-Perot sensor has a rather complex structure, thereby resulting in rather high cost of an ultrasonic detection device is solved. In the sensor, a quartz diaphragm located on one end of a cylindrical support structure and an optical fiber insert core embedded in the support structure form an enclosed extrinsic optical fiber Fabry-Perot chamber. A laser outputted by a DFB laser device that is in the ultrasonic detection device comprising the sensor is inputted to the sensor via an optical coupler. A feedback optical signal by the sensor is converted into an electric signal via the optical coupler and a photoelectric conversion module, and is then sent to a digital signal processor by a data acquisition card. A laser control signal outputted by the digital signal processor is sent to the DFB laser device via a DFB laser control system. The extrinsic optical fiber Fabry-Perot acoustic emission sensor and the ultrasonic detection device comprising the same are applicable to the technical field of ultrasonic detection in a liquid medium.