Abstract: Nowadays,soft rocks easy to weather have been widely used in the construction of earth-rock dams.The change of water content and temperature may lead to the deterioration of mechanical characters of rockfill during the dam’s long-term operation.Further more,acid rain may affect the mechanical characters of rockfill more and more strongly with the deterioration of air and environment pollution around the world.Usually,the life-span of rockfill is much longer than the service-span of dams,but sometimes the mechanical characters of rockfill may change greatly in short time even in several months.The deterioration may lead to the decrease of strength of rockfill and the stability of dams,and it may cause additional deformation of dams.At present,only the weathering status of rocks is considered in the dam design.The rocks are merely divided into wholly-weathered,strongly-weathered,slightly-weathered and so on.The effect of weathering on the life-span and the function of rockfill after construction is seldom considered.With the progress made in environmental geotechnical engineering,the transformation from qualitative description to quantitative research may come true in the researches on weathering.A new constitutive model takeing rock weathering into account based on the single line method or double line method is put forward.It could be applied in the quantitative analysis of the change of the stress-deformation characters of dams during their life-span.The principles of utilizing soft rockfill are also discussed.