The invention relates to a piston type hydrargyrum optical fiber Bragg grating tilt angle sensor and a using method of the piston type hydrargyrum optical fiber Bragg grating tilt angle sensor, and belongs to the technical field of photoelectron measurement. The piston type hydrargyrum optical fiber Bragg grating tilt angle sensor comprises a mercury column metal shell, mercury, mercury column supporting frames, an outer shell, an optical fiber lead-out hole, a leading-out optical fiber, a pressure transmission piston, a dowel bar, an optical fiber Bragg grating, an equal-strength cantilever beam, a cantilever beam supporting pillar and a base. The tilt angle change of a target measured by the sensor is calculated according to the relational expression of the central wavelength difference value delta lambada B of the optical fiber Bragg grating arranged on the upper wall and the lower wall of the equal-strength cantilever beam in a bonded mode and the tilt angle theta of the sensor. The piston type hydrargyrum optical fiber Bragg grating tilt angle sensor and the using method can improve tilt measurement sensitivity of the sensor and enlarge the measurement range of the sensor, the sensor is high in electromagnetic interference resistance and corrosion resistance, and is suitable for long-term monitoring of a side slope; and the sensor is simple in structure and convenient to operate.