To solve the insufficient of current soft mattress in the lower Yangtze River waterway regulation project,we put forward a new concrete cell block D type soft mattress,establish the catenary model to analyze mechanical properties of soft mattress,calculate the soft mattress anti-overturning stability,anti-sliding stability and anti-floating stability,and contrast the adaptability to terrain of the routine soft mattress with the new type.The results show that the new structure obviously improves the safety of water sinking and discharging process and the adaptability to complex terrain.It can provide theoretical support for soft mattress sinking project in complex condition.