The invention discloses a spark discharge gap triggering device and method for series compensation. An energy-taking capacitor is serially connected with a voltage-dividing capacitor and then parallelly connected with a series compensation capacitor. Plasma spraying equipment triggering spark gap discharge is connected with the energy-taking capacitor. During normal operation of a power transmission line, the voltage of a capacitor bank is low, the energy accumulation requirement of the energy-taking capacitor cannot be satisfied, and the energy-taking capacitor cannot be triggered effectively. When a line fault occurs, due to the fact that the amplitude of the current passing the line is large, the voltage of the capacitor bank rises fast, the voltage of the energy-taking capacitor correspondingly rises fast, and the energy accumulation of the capacitor can reach reliable triggering set value, if a relay protection triggering signal is received at this moment, the energy-taking capacitor discharges to supply power for the plasma spraying equipment, and plasma can be sprayed to allow the spark gap to be broken through reliably so as to form protection.