Abstract: In this paper，using 1∶1 000 000 soil data set，the soil attribution database in the Wanjiazhai basin of the Yellow River was built through the soil texture conversion and calculating a part of soil parameters by SPAW procedure．Using 1∶100 000 land use/cover data，the vegetation type in the study area was divided into nine，which were mixed forest land，pasture，water，residential，residentiallow density，industrial，bare land，combining wetland and agriculture．Basing on that，the vegetation type database was built．Using meteorological observed data of 7 meteorological stations from 1977 to 2006 in study area，weather generator were generated by statistical method．Using measured daily runoff data on the hydrological stations of Toudaoguai and Wanjiazhai and meteorological observed data of 7 meteorological stations from 2000 to 2009 in study area， hydrological and meteorological data sets were built，Also Using DEM (digital elevation model) and GIS/RS technology，the data of water cycle space distribution was obtained，522 HRU (Hydrologic Response Units) were divided at last．On the basis of all these，the hydrological model based on the SWAT (Soil and Water Assessment Tool) model in the Wanjiazhai basin of the Yellow River was built．Also month and day runoff was simulated by SCS runoff method with the actual measurement data of day runoff on the hydrological stations of Toudaoguai and Wanjiazhai from 2000 to 2009，in which 2000 to 2006 was taken as the calibration time and 2007 to 2009 was taken as the validation time．In the calibration time，47th subbasin was chose，namely incoming flow of Wanjiazhai，the systematic sensitive analysis and calibration were taken by LHOAT algorithm which based on LH (Latin Hypercube) sampling and OAT (One factor At a Time) sensitivity analysis．Through sensitive analysis and calibration of month scale，10 system parameters were chose，which were Alpha_Bf，Ch_K2，Ch_N，Cn2，Esco，Gw_Delay，Gw_Revap，Gwqmn，Sol_Awc and Sol_K．And through which of day scale，6 system parameters were chose，which were Alpha_Bf，Blai，Ch_K2，Cn2，Esco and Sol_Awc．Also，the simulation system was verified according to measured daily runoff data from 2007 to 2009．Through analysis of simulation，calibration and verification to month/day runoff process in the Wanjiazhai basin of the Yellow River from 2000 to 2009，at the same time，uncertainty of the incoming flow which was induced by the manmade factors such as dam，poling，levees，irrigation，etc was considered，the results showed that this system on the structure was reasonable，the correlation coefficient reaches more than 0．97and Nash-Sutcliffe model efficiency coefficient reached more than 0．96 not only in the calibration time but also in the validation time．The result was good in the simulation process of 2000 to 2009，which could reflect the change of runoff in the study area．And the effect of month runoff simulation is better than that of day runoff simulation．In addition，putting the numerical forecast model and the simulation system coupled，runoff forecast and analysis were done through taking elements forecast of T639 numerical forecast model as inputs of meteorological elements of this simulation system，the result was still good．In general，the simulation system could reflect the inflow runoff process perfectly．Therefore， the simulation result could provide a positive reference of comprehensive utilization of water resources and proper reservoir operation for the Wanjiazhai basin of the Yellow River．

Key words: rainfall runoff, sensitivity analysis, calibration, numerical forecast model, meteorological elements