Abstract: To meet the need of kicking off and compound drilling, the single-bending screw drill tool is often required. However, because of the small diameter of casing, and the structure bends of screw drill shell, whether the screw drill can trip through the casing of the well head section is an important issue at the moment. It is significant to study the mechanical characteristics during the screw pass through the casing in the well head, for appropriately selecting the screw drill. The finite element method was taken to analyze the stress distribution law when the 172 mm single bent screw drill trip into the 244 mm casing, and the effects of bent angles on the running process. The results showed that when the structure bends was less than 2.5°, the 172 mm single bend screw drill was able to trip into 244 mm casing by itself, while when the structure angle of the screw drill is greater than 2.75°, additional external force was need to press the screw drill into the casing.