The invention discloses a multi-gap lightning-protection insulator used for an alternating-current overhead transmission line. The multi-gap lightning-protection insulator is formed by combining an arc blowing structure consisting of a multi-gap arc extinguish chamber system and an insulating material with a composite insulator chain with a certain length. During normal operation of an electric power system, the multi-gap lightning-protection insulator is the same as a long rod suspension insulator in function to achieve mechanical supporting and electric potential isolation effects; when overvoltage generated in the transmission line reaches a certain value, tandem multiple gaps are punctured, an arc passage is established, an arc is stretched by using high temperature and high voltage generated by the arc at the same time until the arc is extinguished finally; the time of duration in the process is extremely short, and action tripping of a relay protection device cannot be caused while lightning current is leaked, so that the reliability of power supply is greatly improved. The function of the insulator and the function of a lightning arrester are combined into one body, so that devices installed on power transmission line poles and towers are greatly reduced.