By taking XK5034 vertical milling machine as the research object, finite element analysis (FEA) of thermal characteristics was carried out through the ANSYS software. The temperature field obtained from the FEA was proved by the actual temperature field obtained from the thermal imager, which discovered that the temperature by FEA was basically same with that from actual measurement. On the basis of this, thermal deformation of the front of spindle was analyzed emphatically under different rotational speed and different environment temperature. The results show that along with increasing of the spindle rotational speed and environmental temperature, thermal deformation of the front of spindle is increased. There is an inflexion point appeared when the environment temperature is at 25 ℃, in the deformation of the front of spindle caused in environment. When the environment temperature is less than 25 ℃, deformation caused by environment temperature has a small relatively impact on the front of spindle. When environment temperature exceeds 25 ℃, the thermal deformation is relatively larger.