The invention provides a preparation method of an aluminum-silicon alloy welding rod for soldering. The preparation method comprises the steps that aluminum-silicon alloy powder and soldering flux powder are evenly mixed and then pressed into a bar billet with the diameter of 20 mm through a tablet press, and then an insulation barrel is placed into a microwave sintering furnace; then a furnace chamber is vacuumized till the vacuum degree in the furnace chamber is lower than 0.1 Pa, then argon with the purity of 99.99% is introduced into the furnace chamber, the output power of the microwave sintering furnace is controlled, the temperature is increased at a certain speed, and heat preservation is conducted; afterwards, the microwave sintering furnace is stopped, so that a sample is cooledalong with the furnace to obtain an aluminum-silicon alloy bar; and finally, the bar is placed into an extrusion die so as to be hot-extruded at a time to make the diameter of the bar reach 3 mm, andthus, the aluminum-silicon alloy welding rod for soldering is obtained. The preparation method is easy and convenient to implement, low in equipment requirement, high in production efficiency, low inenergy consumption and suitable for industrial production; and the welding rod has the advantages that the wettability of the welding rod is as good as that of base metal, and the soldering strength is high.