The invention relates to an installation device for an optical overvoltage sensor of a power transmission line, and belongs to the technical field of voltage measurement. The installation device comprises an L-shaped connection plate, voltage equalizing balls, a support pipe and a sensor fixed housing. The vertical arm of the L-shaped connection plate is connected with a power transmission line through a connection wire and is provided with the voltage equalizing balls. The horizontal arm of the L-shaped connection plate is relatively fixed on fittings on an optical fiber insulator. One end of the support pipe is pressed into a flat shape. The middle part, which is relatively fixed on the fittings on the optical fiber insulator, of the support pipe is cylindrical. The sensor fixed housing sleeves the support pipe. An optical field sensor is arranged in the senor fixed housing. An optical fiber in the optical fiber insulator penetrates through a soft pipe and then is connected with an optical overvoltage sensor through a flange fixed on the sensor fixed housing. By use of the installation device, the circuit is not transformed too much, so construction and installation are convenient; and the surface field is smaller than the corona inception field, so effects of electronic coronas on measurement are avoided and a coupling disturbance problem of the space electric field is solved.