HB is a conserved gene that was selected by the ancestors of the PACMAD group during the high temperature era 49 million years ago. The PACMAD group includes the subfamilies of Triangulariinae, Arundinae, Centurinae, Pennisetum, Pennisetum and Paniculaceae. The invention screened and obtained HB gene which is unique to Pacmad group of Gramineae, because plants compete for light resources by raising plant height and biomass in high-temperature tropical environment, the HB gene, which was selected by our ancestors during the Earth's high temperature era. It can further improve the photosynthetic capacity, carbon and nitrogen use efficiency and high temperature tolerance of plants, thus helping to increase crop yield.