The invention relates to a quantitative estimation method of a hilly region seasonal stream length. Needed hydrometeorology data and hydrogeology data are collected; water subsiding process data is extracted; a water subsiding graph is drawn and subdivided; upper and lower borders of the water subsiding graph are judged; a relation curve between a stream length and a water-contained layer saturated thickness is drawn by a trial method; and finally, a value range of the stream length is quantitatively estimated according to the curve. The method mainly depends on actual measurement of the water subsiding run-off data, adopts simple formula and schema methods, is excellent in operability and actual application value, provides technical support for analysis of hilly region seasonal stream hydrological characteristics, and can reasonably and quantitatively estimate seasonal stream lengths in hilly regions under different abundant and dry hydrological conditions.