Biomass is an important trait in forage sorghum， and positively correlates with plant height. In this study， two functional SNPs of the plant height associated gene SbPH11 were screened from 237 sorghum inbred lines. Three haplotypes， named SbPH11-Hap1， SbPH11-Hap2 and SbPH11-Hap3， at the SbPH11 locus with different combination of the two SNPs have been identified. The plant height of SbPH11-Hap2 materials was extremely significantly higher than that of SbPH11-Hap1 and SbPH11-Hap3 materials， and that of SbPH11-Hap1 materials was extremely significantly higher than that of SbPH11-Hap3 materials. The KASP marker that associates to plant height was developed based on two functional SNPs of the gene SbPH11. The marker was used to genotype and phenotype of 30 sorghum germplasms resources. The KASP marker was confirmed to accurately identify two functional SNPs of SbPH11. These results suggested that the newly-developed KASP marker can efficiently and accurately predict the plant height in sorghum germplasm resources， and can be applied in early screening and molecular marker-assisted selection in breeding for sorghum with higher plant height.