The invention belongs to the field of power systems and especially relate to a large-capacity power transmission line strain tower strain measuring device characterized by comprising a fiber signal modulating-demodulating device and a plurality of measuring sensors. A pulse signal modulator converts a continuous spectrum output by a tunable laser into a pulse signal to be output under the control of a signal generator. The pulse signal enhanced by an erbium-doped fiber amplifier enters the measuring sensors via a circulator. A pulse signal reflected by the measuring sensors enters a high-speed signal receiver via the circulator so that photoelectric signal conversion is achieved and the signal is sampled by a control computer. The large-capacity power transmission line strain tower strain measuring device is applicable to long-term measurement in various complex environments. The measuring sensors are resistant to electromagnetic interference and do not require an operating power supply. A distributed sensor network formed by the large-capacity power transmission line strain tower strain measuring device solves a problem that a conventional wavelength division multiplexing sensor network is small in capability and limited in distributed measure range, and may easily achieve spatial positioning of the measuring sensors.