At present

according to the soil-water retention curve

the matrix suction of soil is mainly obtained by moisture content

which neglects the influence of density on matrix suction. This is imperfect both in theory and in application. Taking the Baqiao Bridge sandy soil for sample

the matrix suction of sandy soil with various densities and moisture contents is tested. After analyzing the test data

the relation between the matrix suction and moisture content in three kinds of densities is got

and taking the density and moisture content both into account

the formula is obtained to determine the matrix suction. The one-dimensional moisture migration test verifies the influence of density on moisture migration. Then this paper finds the changing law that the matrix suction changes obviously with density especially in low moisture content. And with the same moisture content

if the density is gradually added

the value of matrix suction first is lowered

then added and finally lowered

this phenomenon is probed into in this paper.