The largescale new energy accessed into a substation would bring in problems of the overload, harmonic and short circuit and then affects the life of power appliances. Therefore, it is of great significance to study the thermal life loss of transformer for the grid economic operation. Firstly, the power loss of the transformer in harmonic current is analyzed quantitatively and the load factor is derived simultaneously. On this basis, the calculation method of hot spot temperature considering the load factor and harmonic distortion rate is given. Then, considering the special case of sudden shortcircuit of transformer, the calculation method for the winding hot spot temperature is improved. Thirdly, the thermal life loss model based on the hot spot temperature of the transformer is established. Finally, the simulation analysis of a 35 kV transformer in included for verification. It is shown that after new energy resources access, the overload operation causes the great increase of the thermal life loss while the harmonic and shortcircuit have little effect on the thermal life.