Abstract: In recent years, the influence of sand and dust on the external insulation of power system can not be ignored, but there are few studies about that at present. In order to study the discharge characteristics in dust environment, the tip-to-plate gap is employed. A sand-dust simulation experiment platform is built to carry out the AC discharge characteristics test. The effects of gap distance and dust duty ratio on AC discharge in tip-to-plate gap are obtained. The results show that when dust duty ratio is small, AC breakdown voltage in tip-to-plate gap decreases with the increase of dust duty ratio. While AC breakdown voltage in tip-to-plate gap increases with the increase of dust duty ratio when dust duty ratio is large. Therefore, it can be considered that there exists a certain duty cycle of sand and dust (about 1%), which minimizes the breakdown voltage of AC gap. It is found that the duty cycle is independent on the gap distance. Furthermore, the simulation model of tip-to-plate electrode gap is built in the finite element simulation software FlexPDE, and the flashover mechanism of tip-to-plate gap in dust environment is analyzed.