Locking system, characterized by comprising a discrimination unit and converting digital phase a filter unit of the digital loop unit and a digital controlled oscillation by the voltage which are connected in turn, so that the discrimination unit and converting digital phase is configured to perform processing discrimination and phase conversion of an IF signal input from an external standard source and an output signal feedback Fo of an oscillator local thermostatic crystal passing through a division frequency to generate a clock signal clk and sign signal is used to indicate a relationship of magnitude between the frequency signal Fi and Fo signal; the filter unit of the digital loop is configured to carry out filtering processing of the clk signal and the sign signal, and generating a forward signal used to indicate that the frequency of the Fo signal is less than the frequency of Fi signal and the delayed signal is used to indicate that the frequency of the signal Fo is greater than the frequency of the signal Fi; unit digital controlled oscillation by the voltage is configured to perform processing oscillation voltage controlled for early signal and the delayed signal generated after processing filtering the clk signal and the sign signal, to implement a lock of Fo Fi signal and the signal.