According to the theory of Yangian algebra,this paper gives spin realization of Y(SL(2)) algebra of two spin-1/2 coupling system in an extra time magnetic field.By constructing transform operator,eigenvectors of this spin coupling system are also given.
Yangian Y(sl(2)) is realized in the bi-spin system coupled with a time-dependent external magnetic field. It is shown that Y(sl(2)) generators can describe the transitions between the ``spin triplet'' and the ``spin singlet'' that evolve with time. Furthermore, new transition operators between the states with Berry phase factor and those between the states of Nuclear Magnetic Resonance (NMR) are presented.