A method and a device for determining sampling rate are provided. The device receives an input signal of SPDIF. The method includes following steps. A plurality of multiple values between a plurality of bi-phase clock frequencies of the input signal and a system frequency are obtained, and a first weighted average and a second weighted average are calculated according to a first filter range, a second filter range and the multiple values. When a first difference is greater than a second difference, the sampling rate is set to a first sampling rate. Otherwise, the sampling rate is set to a second sampling rate. The first difference and the second difference are obtained according to the first weighted average, the second weighted average and a frequency threshold. The method determines the sampling rate rapidly according to weighted averages adjusted by filter ranges, reduces a probability of erroneous judgment and saves memory.