To study the development of distraction at the fracture site according to inaccurate insertion of the distal screw in treatment of femoral shaft fracture with interlocking intramedullary nail, we prepared 24 femoral bone model, fixed them with interlocking intramedullary nails after artificially making transverse fracture or spiral fracture at mid 1/3 of femoral shaft and distal 1/3 of femoral shaft. The cephalocaudal insertion angles of the distal screws ranged from 5.2 to 45.4. As the insertion angles increased, the distances between the fractured sites ranged from 0.1 to 8.2mm. Distractions splited more than 5mm were seen in the average insertion angle of 34.3±9.4 (28.2-45.4 ). When the insertion was made few millimeter proximal from the center of the distal screw hole, which was parallel to the transverse section of the femur model, fracture distraction ranged from minimum 1.8mm to maximum 5.0mm. In conclusion, the cephalocaudal insertion angle or location of the distal screw can be reason for the distraction between the fractured sites in internal fixation with intramedullary nail in long bone like femur. To prevent the distraction of fractured site, it is important to make the insertion of the distal screw parallel to the transverse section of the femur and to insert into the center of the screw hole.