In summer, the temperature is very high inside vehicles parked under the hot sun. This causes consuming more fossil energy to power the air conditioner and generation of harmful gases. There is currently no effective method to address this problem in an energy-saving and environmentally friendly manner. In this paper, a novel solar-powered air-cooling system for vehicle cabins is proposed based on Phase-change Materials (PCMs); the system prevents the temperature inside a vehicle cabin from rising too high when the vehicle is parked outdoor exposure to the sun. The proposed system consists of three main parts: a solar-energy collection module, power storage module and phase-change cooling module. The solar panel converts solar energy into electricity, and the power-storage module stores the electric energy in a supercapacitor that provides power for the phase-change cooling module. Heat exchange between cabin ambient air and the PCMs is conducted in the cooling module to generate cold air. The proposed system is demonstrated through thermal simulations, which show the long duration cooling effect of the system. Temperature drops of 30 degrees C were obtained in field tests, predicting that the proposed cooling system is beneficial and practical for cooling vehicle cabins.