Polyamides include aliphatic polyamides and aromatic polyamides. 70 years of the 20th century, mainly the application of aliphatic polyamides, such as nylon-4, nylon-6 and nylon-66 film; currently the most used is aromatic polyamide film. The membrane materials are aromatic polyamides, aromatic polyamide-hydrazides and some nitrogen-containing aromatic polymers. Aromatic polyamide membrane to adapt to the pH range can be wide to 2 ~ 11, but the water free chlorine is very sensitive.