Abstract: To meet the need for engineering project, the disturbed and undisturbed soil samples were taken from the Laoying part of Huaihe Dam and the characteristics of shear creep and tensile creep of soil from the dam body and its foundation were studied in laboratory. The creep shear strength (C ) of clay is far lower (about 40%) than the instantaneous shear strength (C); Under the condition of same moisture, the long term tensile strength of clay is larger than the instantaneous, and the long term strain is much larger (about 2 times) than the instantaneous. The maximum depth of tensile crack in dam influenced by coal miming settlement was calculated by using the long term strength indexes of soil mass and was controlled by tensile strain. The cracking damage of dam body is predicted from the data obtained by a linear strain observation system to safeguard the dam.