We study the polarization of the anti-Lambda particle in polarized high energy $pp$ collisions at large transverse momenta. The anti-Lambda polarization is found to be sensitive to the polarization of the antistrange sea of the nucleon. We make predictions using different parametrizations of the polarized quark distribution functions. The results show that the measurement of longitudinal anti-Lambda polarization can distinguish different parametrizations, and that similar measurements in the transversely polarized case can give some insights into the transversity distribution of the antistrange sea of nucleon.