The invention relates to a digital synchronous sampling method, which belongs to the field of D/A mixed signal processing. The method comprises the following steps of: setting a sampling frequency fsto M*N*f0, sampling an input signal with a frequency fi according to the sampling frequency fs, wherein f0 is the frequency theoretical value of the input signal; measuring the frequency of the inputsignal; and subjecting the sampled signal to lower decimation filtering at a decimation position p and a decimation rate M' by a cascade comb decimation filter manner according to the frequency measurement result to an input signal with a sampling frequency and a frequency of fi after decimation satisfying the synchronous sampling relationship. The invention has the advantages of less calculationamount, easy implementation, accuracy synchronization and good practicality.