Abstract: Aiming at the 2D path planning problem of bevel tip flexible needle in soft tissue,an improved unicycle kinematic model is proposed for the flexible needle based on its motion characteristics,and the forward kinematics is calculated using screw theory and product of exponentials formula.The feasibility of linear puncture path is proved from the view of kinematics.Based on this kinematic model,a path planning algorithm adopting multiform paths is proposed,and the optimizing objective function is established taking into account the optimization of needle insertion pose.Then the optimal calculation,simulation and experimentation of the needle puncture path are performed in the environment with obstacles. Results show that this algorithm can effectively optimize the whole paths and make the needle steer clear of obstacles and reach the target precisely.All the errors in the experiments are within 2 mm,which proves that the kinematic model proposed accords with the actual paths.