In recent years, with the standardization of millimeter wave communications, related communication technologies have been widely used, and the quality of millimeter wave communication signals has also attracted attention. Error Vector Magnitude (EVM) is a crucial indicator to measure the quality of transmission signals, and the measurement and calibration of EVM are particularly important. Compared with traditional measurement methods of sub-6 GHz signals, EVM measurement and calibration of higher-frequency broadband wireless communication signals still have complex problems such as inaccurate measurement and large errors. This paper innovatively proposes an Over-The-Air (OTA) measurement method for the first time for EVM parameters of W-band broadband modulation signals based on electro-optical sampling (EOS) technology. This method can not only avoid the nonlinear distortion introduced during down-conversion processing of the received signal but also solve the problem that oscilloscopes and vector signal analyzers (VSA) cannot fully meet the frequency measurement range of high-frequency broadband modulated signals, which provides a new idea for EVM parameter measurement of W-band signals.