The invention discloses a preparation method for photovoltaic back plate glass used for a thin-film solar cell. The preparation method comprises the following steps: selecting glass with a high strainpoint as a glass substrate, wherein the strain point of the glass with the high strain point is greater than or equal to 575 DEG C and the softening point is greater than or equal to 800 DEG C; and sputtering and growing a SiN film layer with a thickness of 80-120nm, a CuZn film layer with a thickness of 50-90nm, a ZnAl film layer with a thickness of 30-60nm, a resistance reducing film layer witha thickness of 15-35nm, an anticorrosive film layer with a thickness of 20-50nm and a Mo film layer with a thickness of 35-65nm on the top surface of the glass substrate from the bottom to the top through magnetron sputtering to obtain the photovoltaic back plate glass, wherein the resistance reducing film layer is a Ti film layer or a Cu film layer, and the anticorrosive film layer is a MoN, MoO, TiN or TiON film layer. According to the invention, the back plate glass obtained by the preparation method has the advantages of the high strain point, no deformation after high-temperature selenylation in a later period, corrosion resistance, low resistivity, small thin-film stress and the like; and the adhesion strength between the multilayer film structure and the glass substrate is high, sothat the diffusion of Na<+> in the glass substrate to an absorption layer is blocked, and the photovoltaic back plate glass has good ohmic contact with CIGS.