The present invention provides a power transmission line mechanical de-icer which comprises a cylinder-shaped jacket whose front end and back end are provided with rope connection structures, a spring guidance mechanism which is slidingly arranged in the jacket, a compression spring whose back end is arranged on the spring guidance mechanism, a hitting head used for hitting the ice which coats a power transmission line, a driving mechanism which is arranged on the jacket and is connected to the spring guidance mechanism and is used for pressing the compression spring such that the hitting head can hit the ice by the elastic potential energy of the compression spring, and a position control mechanism which is used for locking or releasing the spring guidance mechanism or the hitting head, wherein the back end of the hit head is arranged at the front end of the compression spring. According to the power transmission line mechanical de-icer, the de-icing need can be satisfied, the line is not damaged, and the operation is gentle and can be carried out repeatedly on the ground for a long time.