An audio mixing device and method are provided. The audio mixing device includes an analog to digital converter (ADC), a converting module, a mixing module, and a down-sample filter. The ADC is adapted to receive an analog signal, and convert the analog signal into a first digital signal. The converting module receives the second digital signal, and adjusts a data rate of the second digital signal according to a data rate of the first digital signal to generate a third digital signal. The mixing module mixes the first digital signal and the third digital signal to output a mixed signal. The down-sample filters down-samples the mixed to output a down-sampled signal.