The strata in the Sargan area of Tianshan Mountains in southwest Xinjiang are extremely fractured and complex. In recent years， many holes have been drilled through broken and lost circulation formation where falling blocks， stuck drilling and hole collapse happened frequently. In reference to a drilling case in this area， this paper introduces the treatment process and cautions for treatment of the serious drilling accident of drilling string falling-off due to breaking of the coring wire line in the fractured complex strata. With analysis of the accident， guided reaming was adopted to deal with the complex accident effectively. As a result， the hole was successfully finished with the required geological data obtained， and some economic losses were recovered.