The invention discloses a method for building an oilseed-rape group model. The method comprises the following steps of S1, obtaining oilseed-rape group field data; S2, obtaining oilseed-rape group indoor data; S3, building a single-oilseed-rape model; S4, building the oilseed-rape group model. The method for building the oilseed-rape group model has the advantages that the field reduced type oilseed-rape group model is built through conversion and reduction to a field in-situ growth state, the trueness of the model is high, errors are small, the modeling workload is low, the method is simple and cost is low.