Abstract: By improved experiment,the swelling pressure test of expansive soils has been carried out with respect to initial variations in dry densities,water contents and vertical pressures.Correlation of swelling pressures to percents swell,dry densities,water contents and vertical pressures have been studied.Results indicate that the swelling pressure vs.percent swell can be taken as linearly related up to about a swelling pressure of 800 kPa;the swelling pressures increase with increase in initial densities while decrease with increase in water contents and vertical pressures.By means of regression analysis,both the swell pressure-initial density relationship and the swell pressure-initial water content relationship are approximately linear,while the swelling pressure-vertical pressure relation is a semi-logarithm linear one.The most sensitive factor to the changes of swelling pressure is the dry density,then the water content and the last the vertical pressure.