The tilt monitoring for OPGW（fiber optic composite overhead ground wire）transmission tower under harsh environment has important engineering significance. In this paper，based on ultra-weak reflected FBG （fiber Bragg grating），combined with wavelength-division/air-division multiplexing，we propose a inclinometer array monitoring technology for OPGW tower. Firstly，the mathematical relation of FBG wavelength，strain and tower angle is deduced theoretically. Then，based on COMSOL finite element simulation，the stress variation of the tower under the condition of wind excitation and uneven tension is analyzed. Finally，the basic parameters of the inclinometer are calibrated by comparison test，and the sensor is applied to a 220 kV transmission tower in eastern inner mongolia province for tilt monitoring，and the preliminary results of tilt monitoring are obtained. The actual monitoring results show that the proposed method can effectively monitor the tower inclination，the strain sensitivity coefficient of the ultra-weak reflected FBG is about 1.2 pm/με，the sensitivity coefficient of the inclination sensor is 51.8 pm/°，and the monitoring results of the tower inclination is about 2.64° under normal circumstances. This method provides a technical reference for multi-parameter health monitoring of OPGW transmission lines and has a strong engineering application prospect.