Influence of magnetic fields on the properties of methane laminar combustion was investigated experimentally. A high downward gradient of the square of the magnetic flux density was applied on methane laminar diffusion flame. The flame surface temperature and NOX concentration were measured by high-precision testing instruments. The flame size was analyzed by specific image raster analysis software. The results show that with the magnetic field intensity increasing, the flame dimensionless length decreases while the dimensionless width and flame temperatures increase. The gradient magnetic field exerts a great effect on the production of thermal NOX in the flame region under 35 mm due to the oxygen paramagnetic force. Compared to one gradient magnetic field, the concentration of NOX at least decreases by up to 60% on average.