By analyzing measuring of basic benchmarks in the case of the benchmarks which elevation is measured has changed or furtheraway from basic benchmarks at hydrometric station，this paper put forword the idea that basic benchmarks has stationary elevation, elevationof basic benchmarks remain constant when measured with different benchmarks which elevation is measured；when the benchmarks whichelevation is measured is far away from the new basic benchmarks,the first elevation used by the new basic benchmarks should be adjusted.