In order to achieve greater drilling depth, a real-time adjustment optimization model of wellhead backpressure was established. The model achieves a real-time and optimal wellbore pressure profile by optimizing wellbore back pressure during the real-time drilling process. Then a greater drilling depth can be achieved. The optimization results under two conditions; constant backpressure and real-time adjustment of backpressure, were compared by examples, and the influence of different drilling parameters on the optimization results of backpressure and maximum drilling depth under real-time adjustment of backpressure was analyzed. Research results show that compared with the optimization results under the condition of constant backpressure, the real-time adjustment model of wellhead backpressure can optimize the wellhead backpressure in the drilling process so that the wellbore pressure profile can better adapt to narrow safe pressure margins, which can achieve greater drilling depth. Moreover, the real-time adjustment optimization model of wellhead backpressure can further reduce the bottom-hole pressure difference, which is conducive to reservoir protection and increase of ROP. Compared with the volume fraction of hollow spheres and displacement, the maximum drilling depth is more affected by the distance between the separator and bit and the density of pure drilling fluid.