Abstract: Several stress-controlled static and dynamic direct simple shear tests were conducted to study the strength characteristics of the soft saturated clay obtained from the South China Sea. The experimental results in this study show that under the condition without initial shear stress, the cyclic strain increases slowly and steadily with the cyclic number when it is less than 5%, and increases rapidly and reaches the failure when it exceeds 5%, thus 5% of the cyclic strain can be the strain failure criterion. Moreover, the dynamic stress ratio has a threshold 0.52 and the soil will never be destroyed when the dynamic stress ratio is less than the value. The cyclic strain would be accumulated to the side of the initial strain under the initial shear stress. Both the static stress ratio and dynamic stress ratio can improve the accumulative pace of the shear strain and decrease the number of cycles to failure, but the effects of the latter are more significant than the former. The strength envelope of 1 000 times to failure is presented, which provides a safety combination of the static and dynamic stress ratio.