The invention relates to an uninterrupted power supply system for a power source of an intelligentized computer. After a power-down signal observation circuit observes whether the power supply signal is suddenly cut off or not, if yes, a power supply battery circuit is started; a 12V storage battery is directly used by switching so as to output 12V direct voltage for the computer, meanwhile, the 12V direct voltage is still converted into the direct voltage which is needed by other groups of computer by a DC/DC converting circuit. Therefore, when the commercial power is cut off, the 12V storage battery can supply power without using an inversion circuit but in a way that only the 12V storage battery is directly switched to the low voltage DC output terminal of the power source of the computer; the output 12V direct voltage is used for supplying power for the computer in one hand, and the 12V direct voltage can be converted into other voltages such as +5V, +3.3 V, +5VSB, and the like, by DC/DC conversion for the computer. As the efficient DC/DC converting circuit technology is adopted, the converting efficiency can be over 90%, therefore, the consumption in the inversion process is reduced, meanwhile, the overall working efficiency of the power source of the computer is improved, the circuit structure applying the method of the invention is simplified, and the cost is lower.