The invention discloses a light distribution method, a light distribution cup and a road lamp using the light distribution cup. The light distribution method comprising following steps: light ray emitted by a light source partially irradiates outside the light distribution cup to composing a direct light composing rectangular main light spot, and partially irradiates onto the inner wall of the light distribution cup and is reflected outside the light distribution cup to compose a reflective ray composing even rectangular overlapping light spot corresponding to the main light spot shape. The light distribution cup comprises a rectangular cup opening and a cup wall provided with a freeform surface design, and the scattering angle of the cup wall reflective ray is same with that of the cup opening ray. The road lamp comprises a lamp pole, the light distribution cup assembled on the top of the lamp pole, a light source is disposed in the light distribution cup, and the cup opening long edge of the light distribution cup is provided in the same direction of the road. According to the invention, light spots are even, and road lamp amount is reduced. The inventive method is suitable for designs of road lamps and relating lamps.