Wind-sand hazard is a common natural disaster in northwest region of China.Minqin

Gansu Province and Yanchi

Ningxia Province

which are the typical areas of wind erosion

were selected to investigate wind prevention by the northwest shelterbelt.The wind prevention of the schistose shelterbelt in farmland with different heights from ground and in different structures were observed and moreover

the windbreak and sand-fix forest that may influence ground roughness were studied.The methods of sample area survey

statistical analysis

and regression model were used in the investigation.We found that the wind prevention of shelterbelt increased along with raising height from ground in valid windbreak distance ; the degree of porosity belt with its wind prevention presented a very significant negative correlation and the related coefficient was 0.941 ; and ground roughness increased with the raising crown density of windbreak and sand2fix forest.Moreover

the function of ground roughness and the crown density of forest was given.Some simple discussions were made according to the above mentioned results.