Abstract: A new gradation equation which can be used to describe continuous gradation is put forward. Basic properties and reflection ability for different soils of the equation are studied, and general applicability of the equation is validated. The study shows that the equation can describe three typical soil gradation curves which are hyperbola, reversed S-shaped and approximate straight line shape, and has a wide applicability of clay, silt, sand and coarse-grained soil. The shape of gradation curve is determined by parameter b, namely hyperbola or reversed S-shaped, and when m is small, the curve is similar to a straight line. The slope of the curve is mainly determined by parameter m, and increases with the increase of m. The equation has more obvious advantages and broader applicability than Swamee's. Gradation curves of artificial blasting rockfill material from six earth-rock dams at home and abroad are studied, indicating that the range of parameters is roughly -0.28<b<0.64 and 0.45<m<0.75.