A temperature-compensated magnetic field sensor based on a hollow core Bragg fiber (HCBF) Fabry-Perot interferometer (FPI) is proposed. The two ends of the HCBF are fused with optical single-mode fibers (SMF) and adhered to magnetostrictive rods. The temperature and magnetic field response can be demodulated by 2 × 2 sensitivity matrix method, achieving multiparametric demodulation of dual parameters. Experimental results indicate that the error rate of demodulated magnetic field is only 1.9%, while the error rate of demodulated temperature is only 0.8%. The ease of fabrication, high accuracy and temperature compensation suggest that the proposed fiber sensor is suitable for practical magnetic field sensing applications.