This ultrafilter adopts dissymmetrieal semipermeable film which is made from macromolecule material with special process. The raw liquid flows under pressure ,inside or out side the film. The macromolecule substance and colloid particles in the raw liquid are clogged at the film suface and are brought away by circulating raw liquid. Then the raw liquid becomes inspissated, and further more, the subtance in liquid is seperated.