Fengning line of the 112 national road,where the climate belongs to the semi-humid and semiarid zone,the vegetation is lower and soil is porous because of its loess parent textile. This road is 58. 4km in length,and 6 ～ 8 m in width,which will be reconstructed to 12 m. Constructing road affects the loss of soil and water only in some fixed period,and the affecting time is different in different part of soil,such as it is l a in pavements,5a in places where soilswere used to road construction,or places where soils were discarded on the road sides and slopes,3a in temporary occupied places. According to the erosion modulus and areas under different condition,before the road was constructed,the loss of soil and water from road making is784. 0 t/a,and will be 1456. 1t/a during constructing period. So,the loss of soil and water from road making is 708. 1 t/a,which is mainly resulted from discarded soils,roadsides or slopes. The measure is building walls to block the discarded soils,and plant trees and grasses in them or in the road sides and slopes.