The invention relates to a method and arrangement of crosslinking or vulcanizing an elongate element, the method including an extrusion step in which a conductor element is coated by a layer of crosslinkable synthetic material and a crosslinking step in which crosslinking reaction is carried out after the extrusion step. The crosslinking reaction is carried out at first in a first heating zone by heating by heating the coated conductor element in a temperature of 550 degrees Celsius or higher. The first heating zone is located downstream of the extrusion step. After the first heating zone the crosslinking reaction is carried further by heating the coated conductor in a temperature of 200-300 degrees Celsius in a second heating zone.