Tool interference causes serious damage to surrounding soft tissue in minimally invasive orthopedic surgery with a milling robot. The objective of this study is to avoid the collision of cutting tool with complicated shapes, and a novel approach of interference-free toolpath generation in a short intraoperative time is proposed. In order to resolve this issue, we propose the following two methods: intraoperative modeling of soft tissues as an interference area and interference-free toolpath generation based on the model. A model is constructed to represent the opening area and the internal tissues by using a 3-dimensional optical position sensor to measure them. Based on the constructed model, interference-free toolpath is immediately determined by the preliminary definition of evacuating direction. The effectiveness of the proposed method is evaluated with artificial models on the system that the authors have developed so far. A tool contact force against the model was measured by a force sensor mounted on the cutting tool. The result revealed that the tool interference was greatly reduced by implementing the proposed method.