An auto-adjusting high accuracy oscillator is disclosed, which comprises: a frequency comparator, for comparing a synchronization signal obtained from a USB host with an oscillation signal obtain from a device; a control tuning circuit, further comprising a counter and an adder/sub circuit; and an oscillating element; wherein a variation is obtained by the counting of the counter while transmitting the variation to the adder/sub circuit to be encoded thereby into a digital code so as to enable the oscillating element to perform a frequency up/down operation accordingly for approaching the synchronization signal successively.