To study detailed quench behavior of cosine theta Nb3Sn high field dipole magnets a 3D simulation program is made using ANSYS finite element analysis program. The simulation program reproduces the detailed end structure, as well as the straight section, based from a CAD file of I-DEAS. It can calculate the thermal and its resulting mechanical stress distribution inside the coil after a quench. Its detailed method is explained. With the present program, quench propagation along the cable length and also azimuthal quench propagation is shown. Animation programs based on this quench program are shown very effective for the detailed quench analysis.