Abstract: 3D horizontal well technology is obviously predominant in solving the limited surface conditions of oil and gas reservoirs, improving the quality of well pattern arrangement, and increasing the overall development efficiency of oil and gas reservoirs. In this paper, four common 3D trajectory calculation models were analyzed, and accordingly the inclined plane circular arc method was selected as the 3D horizontal well calculation model. Then, the form of 3D horizontal well trajectory was optimized and the six-stage horizontal well design method was put forward to overcome two major uncertainty factors, i.e., the vertical depth of oil reservoir and the buildup rate. This method was applied in Well JH17P25, whose total depth is 2 235 m, offset 425 m, adjusting azimuth length 347 m and offset azimuth 49.30°. Its field construction is smooth with high trajectory coincidence rate and the uncertainty of oil reservoir vertical depth is overcome. Obviously, its application effect is good. It provides the valuable experience for the subsequent design and construction of 3D horizontal wells.