The invention discloses a dynamic pressure detection system and a method based on fiber grating Stokes parameters. The system comprises a tunable laser, an electric polarization controller, a sensing fiber grating, a polarization detection module, a signal processing module, a feedback module and a display unit, wherein the tunable laser emits laser of a certain wavelength and feeds the laser to the electric polarization controller and to the sensing fiber grating; the online polarization detection module acquires laser transmitted from the sensing fiber grating, the laser is outputted to the signal processing module, and three Stokes parameters for the polarization state of the transmitted laser are obtained; and the signal processing module feeds back the parameters to the electric polarization controller to adjust the polarization state of incident laser. Linear birefringence is generated by the fiber grating under effects of external pressure, three parameters for the transmitted laser are caused to change, a single-wavelength source is adopted to realize real-time sensing on the size of the dynamic pressure, the defect that the traditional method is not suitable for small pressure sensing can be overcome, and the defect that the sensing method based on the grating polarization parameter maximum value is not suitable for dynamic pressure sensing can be solved.