Aiming at the complicated problem of laying the soft mattress,the theoretical analysis is carried out,and a simple and effective calculation method of the soft mattress force is obtained.Based on the Characteristic of the Yizheng waterway regulation project of 12.5 m deepwater channel from Nanjing in the Yangtze River，the performance of ship equipment and the quality control technology of the ultra-long soft mattress under complex flow condition are improved,and the working efficiency of the software and the precision such as underwater positioning of the drainage and the overlap width are improved.