Abstract: To control the construction quality of highway is the key measure for its safe work in future. One highway under construction was taken as an example, road radar and dielectric instrument were used at some testing segments, normal methods were carried on at the road, such as sand cone method at the subgrade and core drilling method at the pavement, and some important conclusions were obtained by comparing the calculated data by road radar with the tested data by the normal methods, which revealed that the dielectric values calculated by road radar and tested dielectric instrument, dielectric values and water content, density and degree of compaction all had good correlations, and the thickness of subgrade and pavement calculated by road radar were almost equal to their actual values tested by the normal methods, that is to say that road radar can be used to control the construction quality of subgrade and pavement.