A surgery assistive system includes an instrument having a tool and a manipulator connected to the tool, a spatial sensor system for detecting spatial information of the tool, and a computer system for manipulating a kinematic state of the manipulator. A method for obtaining surface information by the surgery assistive system includes the steps of: defining a target region and a plurality of reference points on a virtual anatomical model of a subject； prompting a user to generate sampling information by using the instrument to sample a plurality of sampling points on the subject corresponding to the reference points； and designating the sampling information as surface information of the sampling points. Each piece of the sampling information includes a coordinate of one of the sampling points, an angle of a contact of the tool at the sampling point, and parameters associated with the contact.一種手術輔助系統，包括一儀器、一空間感測器系統及一電腦系統，儀器包括一工具及一與工具連接的操縱器，空間感測器系統用於檢測工具的空間資訊，電腦系統用於控制操縱器的運動狀態。還提供一種藉由所述手術輔助系統獲取表面資訊的方法，包括以下步驟：在受術者的一虛擬解剖模型上定義一目標區域及複數參考點；提示使用者使用儀器在受術者身上採集與參考點對應的複數採樣點以生成採樣資訊；及指定採樣資訊作為採樣點的表面資訊。採樣資訊包括採樣點的座標、工具在採樣點的接觸的角度及與接觸相關的參數。
