A new photonic crystal fiber sensor based on surface plasma resonance (SPR) effect and defect coupling mechanism is proposed. Two air holes of photonic crystal fiber cladding in the sensor are filled with magnetic fluid material. One hole is coated with metallic thin film on inner layer，and the diameter of the other hole is changed to form defect. By analyzing the relationship among refractive index, temperature and magnetic field of magnetic fluid, the simultaneous measurement for temperature and magnetic field can be achieved. Results show that the coupling resonance peak and the SPR loss peak are blue shifted as temperature increasing and red shifted as magnetic field increasing. The temperature sensitivity of the coupling resonance peak and the SPR loss peak can reach -1.338 nm/℃ and -1.575 nm/℃ respectively, and the magnetic field sensitivity of them is 4.333 μm/T and 2.816 μm/T respectively. The proposed sensor not only has a high sensitivity, but also can achieve accurate measurement for magnetic field and temperature.