Abstract: Surgery simulation has been found very useful in surgery planning and training. In order to obtain a physically realistic surgery simulation, it is needed to treat the deformation of soft tissues with non-linear elastic properties and changeable topologies in real time. Most of the real-time approaches to soft tissues deformation used so far, however, have less such functions. In this paper, an improved algorithm, called Hybrid FEM, is proposed to include the two vital factors into a unified framework, which generalizes the use of FEM in surgery simulation. Since the effects of non-linear properties and topology changes on the deformation of soft tissues often appear locally around the operating positions, only the model of FEM for that limited region should be updated as the operation is performed; while the model for other regions can be kept constant. The Hybrid FEM algorithm has been implemented and examples are given to show the validity of the algorithm.