Excitation equipment is critical to nuclear power plants. To ensure reliable operation of excitation equipment is very important for generation reliability. Some shortcomings appear in the excitation room ventilation and cooling system, which cause uneven temperature and hot points in the excitation room. High temperature of inlet air challenges excitation equipment. An external circulating modification is performed, which makes up the shortcomings of original ventilation and cooling system. This paper describes characteristic of excitation equipment, shortcomings of original ventilation and cooling system, modification plan and its effects.