Magnetization measurements have been performed as a function of wire length L for two series of NbTi multifilamentary wires of interfilamentary spacing 0.20 and 0.39 pm. The magnetization of the multifilamentary wire is made up of two components; one due to the superconducting filaments, /kfi, and the other arising from the interfilamentary proximity couplings, IMP. The filaments are so fine that the end effect can be neglected with respect to the magnetization /Lfi. Then the dependence of the magnetization on wire length mainly results from the proximity-induced magnetization I&, which can be determined as the twist-pitch dependent part of the magnetization. For wires which are relatively short compared with their diameters, flux line movement along the wire axis through the weak superconducting matrix exerts a significant influence on the field distribution and the proximity-effected magnetization A$, will be reduced considerably in comparison to that of the long wires. In this paper the two dimensional critical state model including the effect of low f3,, is developed. Characteristic penetration fields of the proximity-effected magnetization A$, in the direction of the wire axis are estimated by fitting with the two-dimensional critical state model and are shown to have a linear dependence on wire length. The shielding current densities both parallel and perpendicular to the wire axis are estimated and compared with those derived from the continuum twist-pitch theory.