A series of water absorbent porous modified polyacrylonitrile (PAN) fibers were prepared using the blends of PAN and various molecular weight of polyethylene glycol (PEG) by wet-spinning process and water bath post-treatment. The chemical structure and morphologies of the modified PAN fibers were studied. The water transportation, water retention, moisture absorption and mechanical properties of the fibers were discussed. Results show that there is no residual PEG in modified PAN fibers after drawing process in hot water bath and post-treatment. With the increase in PEG molecular weight, the fiber surface grooves become deeper, the inner pore size increases, while the mechanical properties decrease. The water absorbing and transferring capabilities of the modified PAN fibers can be improved in varying degrees due to the different pore structures left by series molecular weight of PEG removing.