Abstract: Based upon the specifications of the extremely narrow-band interference filters in DWDM systems, it is indicated that application of λ_0/4 regular thin film assemble is the most optimal choice in production of such filters. Also, the different layer sensitivity distrbution and the error created in specific layers are analyzed, and random error simulation for several layers is given. Through the investigation into error compensation mechanism in direct turning point monitoring method, it is pointed out that turning point method is up to date the effective way to manufacture such filters, and two types of possible systematic errors are discussed in the end.