Abstract: Spiral borehole is a common drilling operation and has many negative effects. When the spiral borehole occurs in the drilling operation,it affects the quality and real-time of LWD (Logging While Drilling) data,and brings many operational difficulties.The spiral correction method can improve the quality of logging data and reduce the negative impact of spiral borehole.But the real-time of LWD is affected. In this paper, the main reason of spiral borehole formation is studied comprehensively by using the theoretical model of drill string bucking under pressure and the analysis method of 3D Finite Element modelling. Based on the drilling case of a deep-sea exploratory well, by comparing the dynamic responses of drilling tools under different BHA (Bottom Hole Assembly) designs and drilling parameters,the generator of spiral borehole can be judged. With this analysis method, the BHA design can be optimized before the tool enters the well to prevent the spiral borehole. At the same time, it can provide suggestions for adjusting operation parameters and reduce the adverse effects caused by spiral borehole.