Abstract: Rising sample rate processing (RSRP) is a necessary pre-processing in some cases for digital sonar. The principle of RSRP, in which the sample ratio of output over input is an integer, is given and the theoretical result is described. It is shown that the performance of RSRP not only depends on the length of the window function but also on the spectrum of input signal. Several algorithms can be chosen to implement the RSRP. It is shown that the method of convolution. by using the zero-paded input signal and the window function is effective. The system simulation have shown a good agreement of theoretical analysis. The algorithm described in this paper is easy to implement by digital signal processing chips. It is also affordable in choosing the input output sampling rate.