The invention discloses a silicon heterojunction solar cell and a preparation method thereof. Wherein the solar cell comprises an n-type crystalline silicon substrate layer; a lightly doped an n-typehydrogenated amorphous silicon buffer layer formed on the upper and lower side surfaces of the substrate layer; a heavily doped p-type hydrogenated amorphous silicon emitter layer formed on the surface of one hydrogenated amorphous silicon buffer layer; a heavily doped n-type hydrogenated amorphous silicon back field layer formed on the surface of the other hydrogenated amorphous silicon buffer layer; a transparent conductive oxide layer formed on the surface of the hydrogenated amorphous silicon emitter layer and the hydrogenated amorphous silicon back field layer; a metal gate line electrodelay including an alloy transition lay formed on at least one surface of a transparent conductive oxide layer, a hydrogenated amorphous silicon back field layer and a hydrogenated amorphous silicon emitter layer; and a copper-containing conductive alloy layer formed on the surface of the alloy transition layer.