  It is an interesting and open problem to trace the origin of the pseudospin
symmetry in nuclear single-particle spectra and its symmetry breaking mechanism
in actual nuclei. In this report, we mainly focus on our recent progress on
this topic by combining the similarity renormalization group technique,
supersymmetric quantum mechanics, and perturbation theory. We found that it is
a promising direction to understand the pseudospin symmetry in a quantitative
way.
