The invention relates to a long-lasting protection coating for a transmission line pole tower and a preparation method thereof, and belongs to the technical field of transmission line pole tower protection. The transmission line pole tower is made of medium-carbon steel. The medium-carbon steel comprises 0.25 wt%-0.50 wt% of carbon. The surface of the transmission line pole tower is coated with a zinc alloy coating. The zinc alloy coating is coated with an epoxy zinc-rich sealing layer and comprises 0.15 wt%-0.25 wt% of Al, 0.20 wt%-0.25 wt% of Si, 0.20 wt%-0.25 wt% of Mg and the balance Zn. According to the long-lasting protection coating for the transmission line pole tower, chromate components are not included, and the environmental protection performance is good; in addition, component improvement is conducted on the zinc alloy coating, and the corrosion resistance of the zinc alloy coating and the corrosion resistance of a medium-carbon steel base material are improved; and in the sealing layer, zinc powder and titanium dioxide are cross-linked together, so that not only is the good corrosion resistance provided, but also the long-lasting protection coating is endowed with the excellent weather resistance.