Magnetization (M) and susceptibility versus temperature (T) and magnetic field (H) of an internal-Sn processed Nb,Sn wire have been studied and the critical M-H-T surface has been plotted. The normalized magnetization vs. applied field has been filled to Kramer's equation. The effective filament diameter is estimated to be larger than the original filament size. Bridging between the filaments is account for the extra hysteresis. The values of X' and X" do not change much with AC amplitude in a certain background field and frequency, but do change with frequencies for a given AC amplitudes. The interfilament coupling is mainly from bridging, not from proximity effect.