A method for green synthesis of uniform- and large-particle-size polystyrene particles, comprising steps of: prepolymerizing styrene at 70□ to 75□ for 1 h to 6 h in advance while stirring, adding divinylbenzene dissolved with initiators to the styrene, and stirring for 10 min to 30 min to obtain oil phase; heating lactic acid or an aqueous solution of lactic acid to 70□ to 80□, adding the oil phase to dispersed phase by a constant-pressure device, maintaining the temperature for 2 h, heating to 80±5□ and then maintaining the temperature for 1 h, and heating to 85±5□ and then maintaining the temperature for 3 h to 6 h, to obtain polystyrene particles with a uniform particle size ranging from 0.7 mm to 2.0 mm.