Normal temperature close-loop-self-circulating (CLSC) evaporative cooling technology is a newly developed concept for the cooling of large electromagnetic equipment, and it can work under a quite low pressure. The local pressure drop of abrupt expansion and abrupt contraction structure in the inlet box of the condenser occupy an important proportion of the total pressure drop of the cooling system and have great impact on the cooling effect, thus it is not only important but also necessary to calculate and predict it. For this purpose, a new analytical calculation method of local resistance of inlet box of the condenser is introduced in this paper, and it can greatly improve the precision of calculation result. And then, an experiment is carried out to validate the result of calculation. The final finding shows that there is an agreement between experimental and calculation results. Thus it may be claimed that the new calculation method can be adopted in calculating the local resistance in the inlet box of the condenser. Furthermore it can do a good work in directing the design of air cooling condenser used in CLSC evaporative cooling electromagnetic equipment.