Abstract: Considering the safety and accuracy issues caused by soft tissue deformation in robot-assisted percutaneous surgery,this paper presents two strategies for robot-assisted needle insertion into porcine liver based on needle insertion force model,structure and force characteristics of porcine liver.The first strategy requires the robot to automatically stop propelling the needle in the moment that the needle enters into the liver,and then continue to propel the needle with the half speed after the liver returns to relaxed state,aiming to minimize the inaccuracy caused by soft tissue deformation and improve surgical accuracy.The second strategy requires the robot to automatically stop propelling the needle if the needle insertion force exceeds"critical line"of the liver force model after the needle enters into the liver,and then continue to propel the needle after troubleshooting,aiming to avoid accidents during the needle insertion into the liver and improve surgical safety.The experimental results verify the effectiveness of our strategies for robot-assisted needle insertion.