The invention relates to a method of entering a strong electric field along an ultrahigh-voltage tension insulator string and a pedal device used thereby. Equal-potential electrician's feet are each equipped with a pedal device, a clamping mechanism of the pedal devices clamps an insulator steel cap, the electrician enters a strong electric field along a tension insulator string in an upright manner, and the feet move forward alternately along the tension insulator string to reach a work position. The pedal device comprises a clamping mechanism, a mechanism for supporting and fixing foot soles, and a mechanism for pressing or lifting the feet to make the clamping mechanism clamp or release an insulator steel cap. Workers can almost enter an electric field in an upright manner, so that the physical power consumption of workers is reduced. Compared with a method of entering a strong electric field in a sitting or squatting manner, workers feel more comfortable and convenient, the labor intensity is reduced greatly, and workers have enough physical power to complete follow-up charged operation work.