Abstract: In the directional drilling construction of D1219mm large diameter pipeline, the reaming process parameters should be reasonably determined while drilling through complex formations of clay, sand and rock, such as the mud dis-placement and the number of reamer nozzles.Taking an example of Jushui River HDD crossing engineering, according to the inadequate mud displacement and unreasonable reamer selection in directional drilling construction, the related drilling engineering formulas were referred to verify the mud displacement calculation in directional drilling crossing engineering and provide the calculation formula of reamer’ s nozzle number for crossing construction specification.The required maximum mud pressure was calculated used Delft equation in directional drilling construction, the calculation results were applied in directional drilling construction in Jushui River, which a reference for future similar design and construction.