The invention relates to an inner seal type cantilever beam fiber grating sensor, which belongs to the field of sensors. According to the inner seal type cantilever beam fiber grating sensor provided by the invention, inner seal holes are formed in a cantilever beam component provided with a fixed end and a stressed end and are used for placing fiber gratings used as sensitive elements; each inner seal hole is provided with two glue injection holes getting through to the inner seal hole from a cantilever beam; a fiber grating area is fixed between the two glue injection holes in each inner seal hole by using an optical fiber fixing adhesive through the glue injection holes. The encapsulated cantilever beam component, a force application rod and a force application rod installation piece are combined to form the sensor so as to be arranged on an object to be detected; when the object to be detected is acted by a force load, a fiber grating demodulator connected with the fiber gratings and a submarine cable monitors the magnitude of the force load through monitoring the change of fiber grating characteristic wavelengths. The inner seal type cantilever beam fiber grating sensor provided by the invention integrates the advantages of the fiber gratings and the cantilever beam structure, can be used for monitoring the force load of an engineering structure in deep water, and has the characteristics of seawater corrosion resistance, high water pressure resistance, simple structure and low cost at the same time.