Thermal and its resulting mechanical stress due to quenches inside the Epoxy impregnated Nb 3 Sn high field magnets are studied with a combination of a quench simulation program, and ANSYS program. We use the geometry of the high field cosine theta type dipole magnets with one meter and 10 meter length. The turns, where quenches started, are excessively heated up, up to 100 K to 300 K, depending on the coil length and time delay. The non quenching turns and surrounding material are not heated substantially. This elevated temperature and its gradient cause the excessive local stress in the quenching conductors and their insulation material. The stress and strain in the conductor as well as in the insulation become excessive, and they are studied using the ANSYS stress analysis.