  We study the helicity distributions of light flavor quark-antiquark ($q
\bar{q}$) pairs in the nucleon sea. The valence quarks are handled by adopting
the light-cone SU(6) quark-spectator-diquark model and the sea $q \bar{q}$
pairs are treated from statistical consideration by introducing the helicity
suppression factors $l_q(x)$ and $\bar l_q(x)$ to parametrize the helicity
distributions of q-flavor sea quark and antiquark respectively, while $\Delta
l_q(x)=l_q(x)-\bar l_q(x)$ represents a combined effect of helicity
contribution due to sea $q \bar{q}$ pairs. From fitting the nucleon
polarization asymmetries $A^N_1$ in inclusive deep inelastic scattering
processes and the single-spin asymmetries $A^{W^{\pm}}_L$ in Drell-Yan type
processes, we find a significant asymmetry between the quark and antiquark
helicity distributions of the nucleon sea. Therefore the quark-antiquark
asymmetry of helicity distributions of nucleon sea $q \bar{q}$ pairs, i.e.,
$\Delta q_s(x) \neq \Delta \bar q_s(x)$, plays an important role for a
comprehensive understanding of the nucleon spin content.
