Abstract: The method of horizontal directional drilling was used in the water diversion connecting project that is from the South-to-North Water Diversion Canal to Boai County, Jiaozuo City. In order to ensure the canal safety, a variety of technical support measures were adopted. The notable issues in aspects of argument of mud replacement schemes, pre-embedded construction of grouting pipe, material ratio selection of replacement cement slurry, performance evaluation on improvement annular mud were expounded. Moreover, the annulus mud displacement construction technology with large diameter horizontal directional drill was put forward, as well as some optimization suggestions.