Abstract: The terahertz signal source is a foundation and prerequisite for the research of terahertz technology, and its performance directly determines the application prospects and development potential of terahertz technology. The wavelength (frequency) parameter is a key indicator characterizing the performance of terahertz signal sources. Based on the principle of Fabry-Perot (F-P) interference, five sets of F-P interference cavities were designed and processed. Meanwhile, a frequency initial judgment module was added in the system to improve the operating efficiency of the system. A scanning terahertz source wavelength meter with a frequency range covering a wide frequency band was developed to realize the testing of the wavelength (frequency) of terahertz electromagnetic signal sources. Simulation and experimental results show that the frequency range can cover 0.1 THz~10 THz, the resolution is better than 0.03 THz@0.1THz, and the applicable power is 0.5 mW~80 mW. The study of the F-P interference terahertz wavelength meter can provide a reliable and effective evaluation method for the development and application of terahertz signal source.