Abstract: During drilling an extended-reach horizontal well, the friction drag and torque is large, cuttings tend to pile up, also it is very difficult to trip in casings and control ECD. Aiming at improving the accuracy of operations above, the real-time drilling assistant decision system can analysis accurately and simulate these data through transmitting the drilling pressure, torque, pump pressure, rotational speed, pump rate and other data from on-site to the server onshore.With the professional software, the technical personnel can quickly provide decision information with high degree of matching on-site, and effectively assist the rig to overcome these difficulties. Therefore, the system plays a very important role in ensuring the safety and efficiency of an extended-reach horizontal well.