In order to intensify QTL fine mapping, map-based gene cloning, functional analysis and molecular marker assisted breeding of the low hydrocyanic acid content trait of sorghum-sudangrass. Using 500 isolated individual clone plants and their parents of diploid hybrid sorghum-sudangrass F2 generation population as materials, QTL mapping of hydrocyanic acid content traits was carried out on the basis of the high-density molecular linkage map of sorghum-sudangrass that had been constructed earlier. Results show that the coefficient of chain under the condition of LOD value > 2.5, a total of hydrocyanic acid content traits related QTLs detected 16, its distribution in jean grass 7 linkage groups LG1, LG2, LG4, LG6, LG7, LG8 and LG10, genetic contribution rate range of 0.87%~39.9%, of which the genetic contribution rate > 20% of main effect QTLs have Qcn2-2, Qcn4-1,Qcn6, Qcn6-1 and Qcn7, a total of five.