The invention discloses a drilling method of a second-spudding horizontal well. The method comprises steps as follows: a, a drill bit with an outer diameter of 346 mm is adopted for first spudding; b, a drill bit with the outer diameter of 222 mm is adopted to complete drilling of a second-spudding vertical shaft section, a drill bit with the outer diameter of 215.9 mm is adopted to complete drilling at a second-spudding inclined shaft section and a second-spudding horizontal section, and well drifting is performed; c, a second-spudding horizontal well cementation and completion integrated string device is tripped in; d, clear water and lead slurry of cement slurry are injected, and tail slurry of the cement slurry is injected; e, 4-5 m<3> of clear water, 2-3 m<3> of a spacer fluid and 2-3 m<3> of clear water are injected; f, a potassium chloride solution is injected to replace mud, a spacer fluid is injected again, and a 41.3 mm setting ball is thrown; g, 50-60 m<3> of the potassium chloride solution is injected; h, waiting on cement setting is performed for 48 h, and second-spudding drilling of the horizontal well is completed. When an inclination angle and the physical property of a reservoir change greatly, locus adjustment in a larger range can be realized, the flexibility is high, the well cementation construction difficulty is low, and the well cementation quality is good.