The invention discloses a device for measuring radial deformation of a cylindrical test piece. The device comprises a base, a stand column, fastening screws, an annular sensor positioning frame and linear displacement sensors, wherein the stand column is installed on the base, the sensor positioning fame is installed on a sliding guide rail of the stand column through the fastening screws, the linear displacement sensors are installed on the sensor positioning fame, the included angle between the axes of every two linear displacement sensors is 120 degrees, sensor portioning sleeves are installed on the linear displacement sensors, sensor positioning screws are installed between the linear displacement sensors and the sensor portioning sleeves, and the linear displacement sensors are LVDT sensors. The device is simple in structure, convenient to operate and low in cost, and achieves the purpose of measuring radial or transverse strain of the cylindrical test piece; accurate centering can be easily achieved, and the force interaction between the device and the test piece does not exist.