The invention relates to equipment for electrochemical measurement and particularly relates to an electrolytic cell device based on online electrochemical measurement of a power transmission line. The electrolytic cell device comprises an electrolytic cell, a fixed clip and the like, wherein the electrolytic cell comprises an electrolyte container with an upward opening, a square separation plate and a workpiece connection part; the square separation plate is located between the electrolyte container and the workpiece connection part and the peripheral edge of the square separation plate protrudes to form a square annular lug boss; the workpiece connection part is a columnar component and a cylindrical through hole is formed along the middle axis of the workpiece connection part; the cylindrical through hole runs through the workpiece connection part and the square separation plate to be communicated to an inner cavity of the electrolyte container. The device has the advantages that a workpiece of the power transmission line does not need to be damaged and adverse effects on the power transmission line are avoided; the safe operation of the power transmission line is guaranteed and the online electrochemical measurement of the workpiece of the power transmission line is realized completely; the practicability is good and the implementation manner is simple and rapid; the aim of rapidly measuring the corrosion speed of a metal component of power grid equipment can be realized.