A method for controlling the building of architecture of gramineous crops and application thereof. The gene CYC U4;1 (Os10g41430) has a specific expression in a rice pulvinus (which is believed to have a specific expression in other gramineous crops), with a CDS sequence as shown in SEQ ID NO: 2, and an encoded amino acid sequence as shown in SEQ ID NO: 3. Also a promoter sequence of the gene, with the sequence as shown in SEQ ID NO: 1. Transgenic lines obtained by cloning a promoter and full-length CDS of CYC U4;1 to pCAMBIA1301 and transferring this into rice Nipponbare are all characterized by having smaller leaf-stem angles than those of wild rice, accordingly, the expression level of the gene CYC U4;1 can be increased or decreased with genetic engineering technology to control the plant architecture development, thereby improving the plant architecture and increasing the density of germplasm.