Abstract: In the backtow process of horizontal directional drilling engineering for big-diameter oil/gas pipelines, mud flotage impacts on the backtow with the increases of pipe diameter. In order to reduce the friction between pipe and formed hole caused by mud flotage and reduce the risk of backtow process, the effect of mud flotage is calculated and analyzed. A counterweight technology with PE pipe water injection and mud density adjustment are used to balance the mud flotage in backtow process. With this technology, the friction area between pipe and the soil is reduced, and so the friction is lowered to 80%. Meanwhile, the risk of hole-wall collapse caused by the extrusion of pipe flotage is also decreased. The flotage balance technology is successfully adopted in horizontal directional drilling engineering of the main canal of South-North Water Transport Project in the Second West-to-East Gas Pipeline with remarkable economic and social benefits.