Abstract: Aim To resolve the ambiguities of range for a medium pulse repetition frequency (MPRF) Doppler radar. Methods\ A PRF was taken as reference, and a look up table was made by storing the differences of residues between the other PRF and the reference on each range cell. After a set of measured ambiguous range values were obtained, the unambiguous range could be got by searching in the look up table, using the differences of residues.Results\ In order to guarantee the global detectability of all targets, the algorithm of de ambiguity was found: a method by using the differences of residues of look up table and its modified style were given.Conclusion\ This look up table method helps to resolve the range ambiguity and is easy to be used in real time.