In order to reduce the inaccuracy of using the monitoring data outside the pit to evaluate the unorganized emission dust source of open pit mine, the circulating accumulation emission model is established. Based on the model, the monitoring data in the pit can be converted into the dust emission from the pit. Main conclusions include: (1) the circulating accumulation emission model is suitable for the dust diffusion process in open pit mine. The model contains three part, which correspond to dust emission, retention and diffusion in open pit mine. (2) The initial value of the dust in the pit before the team operation has little influence on the final stable value. (3) The dust background value of surrounding environment monitored outside the pit can not be directly used. When the dust enters the pit, it will accumulate under the action of eddy current. To eliminate the effect of background value, the monitoring data should be subtracted by the accumulated value. (4) The dust emission from the pit can be calculated in a certain monitoring period based on the circulating accumulation emission model. Hence the dust emission assessment of open pit can be completed more efficiently based on this model.