The invention discloses an aging resistant backside silver paste used for the crystalline silicon solar cells and a preparation method thereof. The paste comprises 40-50 parts by weight of silver powder, 1-10 parts by weight of nanosized copper powder, 2-10 parts by weight of lead-free glass powder, 35-55 parts by weight of organic binder, 1-5 parts by weight of other additives. The preparation method comprises the following steps: preparation of an organic binder; preparation of lead-free glass powder and preparation of an aging resistant backside silver paste. Application of the aging resistant backside silver paste used for crystalline silicon solar cells prepared in the invention may results in a dense electrode conductive layer, excellent welding properties and a distinct advantage in aging resistance.