  We present a new total intensity image of M31 at 1.248 GHz, observed with the
Five-hundred-meter Aperture Spherical radio telescope (FAST) with an angular
resolution of 4 arcmin and a sensitivity of about 16 mK. The new FAST image
clearly reveals weak emission outside the ring due to its high sensitivity on
large-scale structures. We derive a scale length of 2.7 kpc for the cosmic ray
electrons and find that the cosmic ray electrons propagate mainly through
diffusion by comparing the scale length at 4.8 GHz. The spectral index of the
total intensity varies along the ring, which can be attributed to the variation
of the spectra of synchrotron emission. This variation is likely caused by the
change of star formation rates along the ring. We find that the azimuthal
profile of the non-thermal emission can be interpreted by an axisymmetric
large-scale magnetic field with varying pitch angle along the ring, indicating
a complicated magnetic field configuration in M31.
