Sweet sorghum (Sorghum bicolor L. Moench) is a promising crop for biofuel and forage production, having strong resilience to multiple stresses and being capable of thriving on marginal land. The main goals in sweet sorghum improvement are to increase biomass and sugar yield. We validated quantitative trait loci (QTLs) controlling plant height, biomass, juice weight and Brix with 181 recombinant inbred lines derived from a cross between Shihong137, a dwarf grain sorghum, and L-Tian, a tall sweet sorghum, under four environments. Seven QTLs for plant height, stem and leaf fresh weight, stem fresh weight and juice weight could be repeatedly identified across four environments. However, three of those major QTLs, qPH7-2, qSLFW9 and qSFW9, had strong epistatic effect. Many QTLs related to biomass production were co-localised with previously known height QTLs, suggesting that plant height is a major trait regulating biomass production. However, qSFW1-2, qSLFW6-1, and qSLFW6-2 were mapped to positions with no known height QTL. We also identified and validated stable qBrix2 across environments. This study provided a genetic basis for integrated approaches, including plant height, to improve sweet sorghum biomass and sugar production.