Abstract: In recent years, with the construction of the first and second West-to-East Gas Pipelines, the diameter of horizontal directional drilling has reached 1 219 mm, so that the subsequent diameter of reamed hole has increased to 1 600 mm plus and the stages of reaming are then also increased, which is easily likely to cause irregular shape of hole profile and result in collapse, sticking and even crossing failure. Analysis shows factors affecting the hole quality include formation properties, reaming differential, reaming diameter, mud properties, bottom hole assembly, the nozzle arrangement of drilling tools and mechanical operation etc. In order to improve the quality of hole profile of horizontal directional drilling, measures such as lightweight drilling tool, adjustment of jet direction of the nozzle, addition of guide at the place drilling tool diameter changed greatly, and optimization of downhole assembly were proposed. This method has been successfully applied in Weihe River crossing construction in the 2nd West-to-East Gas Pipeline Project. The level of hole quality control has been increased significantly. The ability of horizontal directional drilling to cross formations with low bearing capacity like coarse sand has been improved, and the construction risk has been reduced.