Aiming at the problem of short coring sample with skirt of φ89mm reverse circulation bit, numerical simulation analysis was made on the breaking process with finite element software ANSYS. According to the analysis results, reasonable design scheme was put forward. The further analysis was made on the new bit with finite element numerical simulation and the comparative analysis and indoor experiment on the original design were carried out. The results indicate that the optimized bit has longer, complete coring sample without skirt.