In this paper, we put forward a method to animate arbitrary topology facial model (ATFM) based on the MPEG-4 standard. This paper deals mainly with the problem of building the FaceDefTables, which play a very important role in the MPEG-4 based facial animation system. The FaceDefTables for our predefined standard facial model (SFM) are built by using the interpolation method. Since the FaceDefTables depend on facial models, the FaceDefTables for the SFM can be applied to only those facial models that have the same topology as the SFM. For those facial models that have different topology, we have to build the FaceDefTables accordingly. To acquire the FaceDefTables for ATFM, we first select feature points on ATFM, and then transform the SFM according to those feature points. At last, we project each vertex on the ATFM to the transformed SFM and build the FaceDefTables for the ATFM according to the projection position. With the FaceDefTables we built, realistic animation results have been acquired.