A novel temperature-insensitive pressure sensor based on fiber Bragg grating (FBG) broadened bandwidth technique using a plane round metal diaphragm is studied theoretically and experimentally. Considering the strain modulating trait of the diaphragm, the smart box structure is adopted and FBG is affixed radially, with the axis center of FBG aiming at the zero strain zone of the diaphragm. Temperature-independent pressure sensing is measured by bandwidth of FBG due to the bandwidth is sensitive to strain but temperature. This approach shows a pressure resolution of ±0.15 MPa and a pressure sensitivity of 0.34 nm/MPa in the range 0～0.75 MPa, with the spectral resolution of the spectral analyzer of 0.05 nm. The experimental results match the theoretical analysis well.