By taking polluted sediment dredging and disposal project of Caohai of Lake Dianchi as an example, assessment factors and focus are identified and analyzed. The environmental impact assessment of engineering on water quality, surrounding landscape, and assessment of smell and noise are discussed in construction periods. Besides, environmental assessment impact points of sediment stockpiling on groundwater, soil and surrounding odor are presented. Based on environmental impact assessment of dredging on surrounding ecological environment in operating period, the points of environmental benefits of dredging project are analyzed. Aiming at the secondary pollution problems produced during dredging, residual water treatment and sediment stockpiling, some practical countermeasures for secondary pollution prevention are pointed out.