Abstract: The 100 000 m³ oil tank, a project intruduced from Japan, has been put into oparation in Qing-Huang-Dao, which is the biggest one in China. To know the and distrbution of stress in it when loaded, and to collect data for oroper desing of such big tanks in the future, stress and stain in it are measured and analysed, which is followed by a proposal as to improving the design of big tanks in China in order to bring down the peak stress in large angle slit bonding area, making it stronger to withstand the low frequency fatigue damage.