Magnetic field was introduced to the experiment of re doping polyaniline (PAn) by sulfasolicylic acid(SSA). Effects of the magnetic intensity, concentration of doped agents and reaction time on the conductivity, solubility and thermo stability of PAn were studied,and the properties of PAn were characterized by four probe, thermogravimetric analysis (TGA), UV Vis and XRD. The results showed that the conductivity, solubility and thermo stability of PAn were obviously improved in magnetic field, due to the effect of the cooperative effect of SSA and magnetic field. In compared without magnetic field that the conductivity was increased from 0.5 s/cm to 3.2 s/cm; the solubility in xylene was also increased from 12% to 23%; and the temperature of thermal decomposition was improved from 220 ℃ to 320 ℃.