The invention provides a preparation method of an ultra-pure and ultrafine silver nanowire. The preparation method comprises the following steps: step 1, an ethylene glycol solution with sodium bromide, an ethylene glycol solution with sodium chloride, an ethylene glycol solution with PVP and an ethylene glycol solution with silver nitrate are prepared, and in the preparation process, moisture inethylene glycol is removed through heating; and step 2, the ethylene glycol is taken, heating is conducted to remove the moisture, the ethylene glycol solution with sodium bromide, the ethylene glycolsolution with sodium chloride, the ethylene glycol solution with PVP and the ethylene glycol solution with silver nitrate which are prepared in the step 1 are added, the temperature is increased to form a nucleus, temperature increasing is reduced, and the ultra-pure and ultrafine silver nanowire is prepared. According to the preparation method, the adsorbed moisture in the ethylene glycol is removed through heating, thus the concentration of hydroxyl plasma in a reaction solution is effectively decreased, seed crystal damage caused by ion etching is reduced, the dynamic process of nucleus forming is adjusted and controlled, the probability that the crystal nucleus grows into the nanowire is increased significantly, and the ultra-pure and ultrafine silver nanowire can be obtained withoutthe need of the subsequent purification process.