The invention relates to an isolation structure for measuring external electric interference signals by the pressure fluctuation of a hydraulic turbine. The method is characterized in that a pressure fluctuation measuring pipe which is vertically arranged and has outer thread is connected with an isolation seat through a pipe hoop with inner threads at both ends thereof, the isolation seat is connected with a pressure fluctuation sensor with outer thread at the top thereof through inner thread, a pipe cavity which is formed by the isolation seat, the pipe hoop and the pressure fluctuation measuring pipe is filled with insulating oil, and the interface of the insulating oil and a water column in the pressure fluctuation measuring pipe is arranged in the pressure fluctuation measuring pipe.The electric interference signals which are transmitted to the pressure fluctuation sensor probably through a measuring pipeline and the measured water are respectively isolated by the isolation seatand the insulating oil, and the insulating effect between the isolation seat and the insulating oil is very good, thus fundamentally solving the influence of the external electric interference signals on the pressure fluctuation sensor.