In order to decrease the computation and storage load

different sampling-rates

together with the Sampling-rate Conversion

are often used in a system.When a signal is analyzed in the fractional Fourier domain

the lower sampling-rate could be adopted than the Nyquist sampling-rate

which means that the traditional sampling-rate conversion theory

founded in the frequency domain

could be disabled under the circumstances.The traditional sampling-rate conversion theory is generalized to obtain the version for the fractional Fourier transform (FRFT).First

the formulas and signification of decimation and interpolation are studied in the fractional Fourier domain.Based on these results

the sampling-rate conversion theory for the FRFT with a rational fraction as conversion factor is deduced.It's obvious that the sampling-rate conversion theory for the FRFT changes to the traditional version when the FRFT order equals π /2.Finally

the theory obtained in this paper is verified by some simulations.