We analyze the principle of wide spectrum film thickness monitoring and design a portable embedded wide spectrum monitoring system of film thickness. This system is based on ARM9 core processor S3C2440 and Linux operating system with real-time monitoring interface developed on cross platform Qt2. The system collects spectral data by the USB fiber spectrum instrument, and the S3C2440 processor processes spectral data by methods such as wide spectral scanning, evaluation function, and single wavelength extremum. Thus the purpose of monitoring the film thickness of optical coating is reached. The testing result of the system indicates that this system has high precision, fast response and convenience in carrying and operating.