A polymer with pores close to a straight line was prepared by adding a plasticizer lactic acid to cellulose propionate. We succeeded in preparing for the porous cellulose propionate (CP) by a low-cost and eco-friendly manufacturing process with water treatment technology. The CP used in this study has a higher molecular weight and better mechanical strength than the cellulose acetate (CA) widely used for the membrane. In general, as the molecular weight of the polymer increases, the mechanical strength can be stronger. Thus, porous CP can be manufactured as a single film without additional polymer support. The additive LA can penetrate into the CP chains and plasticize the membrane to form pores. The manufactured membrane was installed in a water treatment machine and hydraulic pressure was applied from 2 to 7 bar. The surface and the cross-section of the membrane were verified using SEM, and the membrane, to which hydraulic pressure was applied with a plasticizer, showed a surface in which pores were generated. Then, FT-IR was investigated to confirm how the interaction between the functional groups between CP and LA changed.