  It has been an interesting question that why there are one-third of Kuiper
Belt Objects (KBOs) trapped into the 3:2 resonance but, in contrast, only
several KBOs are claimed to be associated with the 2:1 resonance. In a model
proposed by Zhou et al. (2002), the stochastic outward migration of the Neptune
could reduce the number of particles in the 2:1 resonance and thus the objects
in the 3:2 resonance become more distinct. As a complementary study, we
investigate the effect of proto-stellar discs on the resonance capture. Our
results show that the gaseous drag of a proto-stellar disc can trap KBOs into
the 3:2 resonance rather easily. In addition, no objects are captured into the
2:1 resonance in our simulation.
