The temperature-insensitive fiber Bragg grating (FBG) dynamic pressure sensing based on reflection spectrum bandwidth modulation and differential optical power detection is proposed and experimentally demonstrated. A specially designed double-hole cantilever beam is presented to locate the FBG into the linear strain-gradient region, resulting in FBG reflection spectrum symmetrical broadening and optical power linear increasing with pressure enhancing. Based on the theory of optical waveguide and material mechanics, the causation of FBG spectrum broadening under the linear strain-gradient is analyzed, and the corresponding force-to-bandwidth broadening relation and force-to-optical power relation are formulized. By replacing the traditional wavelength demodulation with optical power detection technique, the demodulating process is simplified and immune to temperature variation. For a temperature range of -10～80 ℃, the measured pressure fluctuates less than 1.8% without any temperature compensation. The system acquisition time is up to 80 Hz for dynamic pressure measurement. The experiment demonstrates the system is stable and applicable.