  We disclose a method to obtain the transverse light-shift along the probe
light of a single-axis alkali metal-noble gas co-magnetometer. The relationship
between transverse compensating field and light-shift is deduced through the
steady-state solution of Bloch equations. The variety of probe light intensity
is used to obtain the residual magnetic field, and step modulation tests are
applied to acquire the total spin-relaxation rate of electron spins and
self-compensation point. Finally, the transverse light-shift is reduced from
-0.115 nT to -0.039 nT by optimizing the probe light wavelength, and the value
of the calibration coefficient can be increased simultaneously.
