This study was carried out to evaluate the performance of the separate membrane (HF; hollow fiber membrane with polysulfone) process applied with the external membrane types, internal pressure membrane types and external-internal types according to the variations of pressure and membrane pore size in the purification treatment process of the lake water. The maximum permeate flux was average values of 282 LMH and 234 LMH with the pore size of 0.3 and 0.05 ${mu}m$ respectively in the external pressure membrane process, and 443 LMH and 522 LMH with the pore size of 0.3 and $0.05{mu}m$ respectively in the internal pressure membrane process. In addition, the maximum permeate flux of the process that was applied with external and internal membrane pressure simultaneously showed the average values of 674 LMH with the pore size of $0.3{mu}m$, and 648 LMH with the pore size of $0.05{mu}m$. Therefore, maximum yield per unit area is supposed when the separate membrane that was applied with external and internal pressure simultaneously are used to treat the lake water.