NOVELTY - A solar back plate comprises inner surface layer, core layer and outer surface layer. The inner surface layer and outer surface layer are made of polyamide resin, filler and additive. The additive comprises antioxidant, UV absorbent and/or light stabilizer. The core layer comprises modified polypropylene resin composition comprising 100 pts. wt. polypropylene resin, 5-50 pts. wt. grafted polyethylene, 0-100 pts. wt. additive and 0-2.5 pts. wt. filler. The grafted polyethylene comprises 100 pts. wt. polyethylene resin, 0.5-1.0 pt. wt. grafting agent and 0.03-0.2 pt. wt. initiator.    USE - Solar back plate used for manufacturing solar battery assembly.    ADVANTAGE - The solar back plate has excellent low-temperature resistance, impact resistance, anti-aging performance and humidity resistance. It meets the required shrinking rate, hot air aging and electrical insulation property. The modified polypropylene resin composition is better than other back plates in terms of water absorption, water vapor permeability and interlaminar peeling.    DETAILED DESCRIPTION - A solar back plate comprises inner surface layer, core layer and outer surface layer at mass ratio of 10-20:20-40:40-60. The inner surface layer and outer surface layer are made of polyamide resin, filler and additive. The additive comprises antioxidant, UV absorbent and/or light stabilizer. The core layer comprises modified polypropylene resin composition comprising 100 pts. wt. polypropylene resin, 5-50 pts. wt. grafted polyethylene, 0-100 pts. wt. additive and 0-2.5 pts. wt. filler. The polypropylene resin is homopolymerized and/or copolymerized polypropylene resin having differential scanning calorimetry (DSC) melting point of 160-168 degrees C and melt flow rate of 1-2 g/10 minutes. The grafted polyethylene comprises 100 pts. wt. polyethylene resin, 0.5-1.0 pt. wt. grafting agent and 0.03-0.2 pt. wt. initiator obtained by grafting reaction. The polyethylene resin is homopolymerized and/or copolymerized polypropylene resin having DSC melting point of 120-135 degrees C and melt flow rate of 1-2 g/10 minutes. An INDEPENDENT CLAIM is included for preparation of solar back plate comprising uniformly mixing polyethylene resin, grafting agent and initiator, extruding by screw melting to prepare grafted polyethylene, uniformly mixing polypropylene resin, filler and additive, extruding by screw melting to prepare modified polypropylene resin composition, co-extruding three layers by screw melting, casting, cooling, performing traction and coiling.