Abstract: Sandstorm occurrence recorded by 12 weather stations by Helan Mountain was analyzed statistically.The maxium data length is 45 years.Monthly variation shows that April and May are the highest occurrence months in a year,its average occurring times is 3.2 and 3.1 respectively.Yanchi is the highest occurrence center at the east side of Helan Mountain area,where the maximum sandstorm occurring times is 5.4 in April,Guaizi Lake is that at the west side with the maximum sandstorm occurring times of 5.2 in May and the second of 5.0 in April.Average annual variation suggests that the sandstorm occuring times is decreasing in general;this comes from afforestation and irrigating engineering.But annual variation showed by Yanchi,Guaizi Lake and Baiyan maodao stations appears a increasing trend,which results from deforestation,overgrazing or not effective desertification control.Although sandstorm occurrence times is decreasing generally in major Helan Mountain area,the strong and extra-strong sandstorms come about increasingly.So the degree of hazard is more severe.The problem of that sandstorm is still the one of main meteorological hazards should not be taken lightly.

Key words: Helan Mountain area, sandstorm, trend