Abstract: The scheme of assimilation of multivariate observation data and crop growth model based on Downhill-Simplex algorithm was established while LAI,dry weight of living storage organs (WSO),total above ground production (TAGP) and soil moisture (SM) as the point of integration for summer maize in Hebei.Correctness verification of assimilation of the observational data and crop growth model was firstly performed.Then,sensitivity of all parameters and initial value of the state variables in WOFOST were analyzed based on the Downhill-Simplex algorithm and the parameters to be optimized were determined through selection of parameter groups and optimizationresults.The optimal value of those parameters was at last obtained by means of optimization of new observed data.So,assimilation of measured data and crop growth model was achieved and simulated accuracy of crop growth model was improved.In addition, parameters to be optimized in data assimilation mainly included specific leaf area,leaf maximum CO2 assimilation rate,the initial total crop dry weight,maximum daily increase in rooting depth,and initial amount of available water in total root zone.

Key words: Assimilation of observation data, Crop growth model, Downhill-Simplex algorithm, Sensitivity analysis