The invention discloses a dynamic traffic flow based forecast method of noise in the peripheral zone of a long straight road. According to the method, a microcosmic moving trajectory of a vehicle in a road section is defined accurately, a vehicle source emission model is established, a noise transmission model is established simultaneously, and a complete set of noise forecasting method is obtained. The forecast method comprises steps as follows: (1), dynamic traffic flow simulation vehicle models at a forecast location are classified, and a dynamic traffic flow simulation model is established; and (2), reference radiation sound levels of different vehicle models are determined, meanwhile, traffic composition, range attenuation and noise barrier insertion loss are considered to calculate forecast sound level of the noise, and the forecast sound level is amended with consideration of surface roughness, the slope and the roadside ground type. According to the forecast method, limitation of the conventional noise forecast method is broken through on the basis that correlation research ideas of other subjects are absorbed sufficiently, and the sound level of the noise in a sensitive area can be forecast accurately.