There may be great difference in tolerance of early and present new type PC to voltage sags due to fast update of PC technique. In the paper, PC power supply and motherboard circuit are analyzed firstly. And the impact on sag-sensitivity of PC is pointed out because of structure changing and embedded solutions. Then an experimental program is developed and Chroma 61860 is used as voltage sag generator. Three mainstream PCs that were produced in different periods are selected as the representatives (two PCs are the same brand and batch among them). Under different operating conditions, sensitivity of PC to voltage sags is researched. And test curves are compared with the existing sag-tolerance range about PC. The results show that the PC operating condition is one of the important factors that affect sensitivity of PC to voltage sags. And the sag-tolerance of present PC has been enhanced markedly.