Optical filters can be used in nearly every field from land to space. To get good performance optical filter, it is important to measure and control the film thickness of every layer on the substrate. There are many methods to monitor thin films' thickness in real-time. The most important one is the optical monitoring techniques. To avoid changing monitoring substrate frequently, we usually change the monitoring wavelength, and judge the film thickness of every layer at shut-turning point of the electric signal that represents the real-time film thickness. In the same time, Computer can be used to auto count the number of the turning point, then shut the electric source and the baffle when the counted number of the turning point arrives at the setting one. The electric signal which represents the real-time film thickness is affected by many aspects, such as optical noise, electric noise deposit rate and etc. It is not easy to judge the turning point accurately. Hence, it is useful to apply Fuzzy logic to judge the Shut-turning point of each layer in the process of manufacturing the optical filters. We design a fuzzy controller for thin film thickness monitoring which considered about both film thickness deposit rate and noise. A table for the shut-turning point judgment is set up in fuzzy logic. Then we can use computer to judge the turning point by looking up the table in real-time. This monitoring system has been applied in many projects to manufacture optical filters and got good results. Therefore, real-time monitoring film thickness using fuzzy logic is a good technique for film thickness monitoring.