Sorghum is a type of forage crops with the most potential of saline-tolerance, which is known for its strong tolerance to high level of salt and alkaline. Biomass is an important trait of forage sorghum and plant height is positively correlated with it. In this study, a KASP marker associated to plant height was developed based on the haplotype of two functional SNP loci of gene SbPH11 using an association mapping population including of 237 sorghum inbred lines. The marker was then used to genotype a subset of the association mapping population and other 30 sorghum germplasms resources, and the results confirmed that the KASP marker could accurately identify the two functional SNP loci of SbPH11. There are three haplotypes in SbPH11: SbPH11-Hap1, SbPH11-Hap2 and SbPH11-Hap3, the plant height of sorghum corresponding to SbPH11-Hap2 was significantly higher than that of SbPH11-Hap1 and SbPH11-Hap3, and the plant height of sorghum corresponding to SbPH11-Hap1 was significantly higher than that of SbPH11-Hap3. These results suggested that the KASP marker can efficiently and accurately predict the plant height of different sorghum germplasm resources, and can be applied to early screening and molecular marker-assisted selection in the breeding for sorghum plant height.