The invention discloses an online continuous detection system of a water content in wellhead output liquid. The system is a real-time dynamic processing system of oil well output liquid, which comprises a signal collector sensor based on the Internet of Things and deployed at the wellhead, a high-speed data collection device and an analysis system deployed on a cloud platform, wherein the signal collector sensor realizes real-time data collection; the high-speed data collection device transmits the data collected by the signal collector sensor to the analysis system in real time; and the analysis system generates result flow in real time after receiving the data. Corresponding to the above system, the invention further provides an online continuous detection method of the water content inthe wellhead output liquid. By adopting the online continuous detection method and system disclosed by the invention, the online continuous detection of the wellhead output liquid is realized, and theproblems of poor adaptability, low detection accuracy, calibration difficulty and the like in the one-well-one-meter analysis mode of the existing water content analysis device are changed.