We study the lepton sector in the model based on the local gauge group
SU(3)c⊗SU(3)L⊗U(1)X which do not contain particles with
exotic electric charges. The seesaw mechanism and discrete A4 symmetry are
introduced into the model to understand why neutrinos are especially light and
the observed pattern of neutrino mixing. The model provides a method for
obtaining the tri-bimaximal mixing matrix in the leading order. A non-zero
mixing angle Ve3 presents in the modified mixing matrix.Comment: 10 page