The invention relates to an electro hydraulic servo system heat balance determination method. Aiming at the heat balance calculation of a servo mechanism, an existing method adopts a servo system as a temperature whole body, energy power is assumed to completely convert into heating, and the heat is absorbed by oil liquid and a structure through heat capacity and is converted into temperature rise. However, component parts of the servo system are more, the temperature difference of the parts is large, and an operating and heating mechanism is complicated, so that the method is hard to accurately simulate the heat property. According to the electro hydraulic servo system heat balance determination method provided by the invention, a servo system is decomposed into a turbine, a tangent pump, a heat exchanger, an overflow valve and other main elements; the elements are divided into flowing nodes and outer wall nodes; heat of each part is calculated; a heat model of the servo motor is built through a heat capacity-heat resistance (R-C) theory; and the heat circularly flows in the servo system along with hydraulic oil, so that the heat of the nodes is mutually affected, and finally the heat balance of the servo system is achieved.